diff --git a/avr/devices/all/includes.asm b/avr/devices/all/includes.asm
index 220c03e..41039f9 100644
--- a/avr/devices/all/includes.asm
+++ b/avr/devices/all/includes.asm
@@ -96,6 +96,21 @@
 #endif
 
 
+
+#ifdef MODULES_COM2W
+.include "modules/com2w/defs.asm"
+.include "modules/com2w/com2w.asm"
+#endif
+
+
+
+#ifdef MODULES_COM2W1
+.include "modules/com2w/defs.asm"
+.include "modules/com2w/common.asm"
+.include "modules/com2w/com2w1.asm"
+#endif
+
+
 #ifdef MODULES_CLOCK
 .include "modules/clock/main.asm"
 #endif
diff --git a/avr/devices/all/main.asm b/avr/devices/all/main.asm
index 3d29c32..8c520a0 100644
--- a/avr/devices/all/main.asm
+++ b/avr/devices/all/main.asm
@@ -135,6 +135,19 @@ onSystemTimerTick:
   bigcall ComOnUart1_Periodically
 #endif
 
+#ifdef MODULES_COM2W
+  bigcall COM2W_Every100ms
+#endif
+
+
+#ifdef MODULES_COM2W0
+  bigcall COM2W0_Periodically
+#endif
+
+#ifdef MODULES_COM2W1
+  bigcall COM2W1_Periodically
+#endif
+
 #ifdef MODULES_TCRT1000
   bigcall TCRT1K_Every100ms
 #endif
diff --git a/avr/devices/all/modules.asm b/avr/devices/all/modules.asm
index 14f405d..b5a3e19 100644
--- a/avr/devices/all/modules.asm
+++ b/avr/devices/all/modules.asm
@@ -81,6 +81,18 @@ initModules:
   bigcall ComOnUart1_Init
 #endif
 
+#ifdef MODULES_COM2W
+  bigcall COM2W_Init
+#endif
+
+#ifdef MODULES_COM2W0
+  bigcall COM2W0_Init
+#endif
+
+#ifdef MODULES_COM2W1
+  bigcall COM2W1_Init
+#endif
+
 #ifdef MODULES_MOTION
   bigcall Motion_Init
 #endif
@@ -223,6 +235,21 @@ runComModules_loop:
       pop r16
       sbci r16, 0
 #endif
+
+#ifdef MODULES_COM2W0
+      push r16
+        bigcall COM2W0_Run
+      pop r16
+      sbci r16, 0
+#endif
+
+#ifdef MODULES_COM2W1
+      push r16
+        bigcall COM2W1_Run
+      pop r16
+      sbci r16, 0
+#endif
+
     pop r17
     ; check for repeat request
     tst r16
diff --git a/avr/modules/com2w/com2w.asm b/avr/modules/com2w/com2w.asm
new file mode 100644
index 0000000..00c38b4
--- /dev/null
+++ b/avr/modules/com2w/com2w.asm
@@ -0,0 +1,664 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+#ifndef AVR_MODULES_COM2W_COM2W_H
+#define AVR_MODULES_COM2W_COM2W_H
+
+
+.dseg
+
+com2w_iface: .byte COM2W_IFACE_SIZE
+
+
+
+.cseg
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W_Init
+;
+; @clobbers 
+
+COM2W_Init:
+  ldi yl, LOW(com2w_iface)
+  ldi yh, HIGH(com2w_iface)
+  rcall NET_Interface_Init                 ; (R16, R17, X)
+
+  ; setup CLK line (as input, disable internal pull-up resistor)
+  cbi COM_CLK_DDR, COM_CLK_PIN           ; set CLK as input
+.ifdef COM_CLK_PUE
+  inr r16, COM_CLK_PUE
+  cbr r16, (1<<COM_CLK_PIN)               ; disable pullup on CLK
+  outr COM_CLK_PUE, r16
+.else
+  cbi COM_CLK_OUTPUT, COM_CLK_PIN        ; disable pullup on CLK
+.endif
+
+  ; setup DATA line (as input, disable internal pull-up resistor)
+  cbi COM_DATA_DDR, COM_DATA_PIN         ; set DATA as input
+.ifdef COM_DATA_PUE
+  inr r16, COM_DATA_PUE
+  cbr r16, (1<<COM_DATA_PIN)              ; disable pullup on DATA
+  outr COM_DATA_PUE, r16
+.else
+  cbi COM_DATA_OUTPUT, COM_DATA_PIN      ; disable pullup on DATA
+.endif
+
+  ; setup pin-change interrupt for CLK
+  rcall com2wEnableClkIrq
+
+  inr r16, COM_IRQ_ADDR_CLK
+  sbr r16, (1<<COM_IRQ_BIT_CLK)           ; enable pin change irq for ATTN line
+  outr COM_IRQ_ADDR_CLK, r16
+
+  inr r16, GIMSK                           ; enable pin change irq PCIE0 or PCIE1
+  sbr r16, (1<<COM_IRQ_GIMSK_CLK)
+  outr GIMSK, r16
+  ldi r16, (1<<COM_IRQ_GIFR_CLK)          ; clear pending irq by writing 1 to ATTN bit
+  outr GIFR, r16
+
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W_Every100ms @global
+;
+; @clobbers R16, Y
+
+COM2W_Every100ms:
+  ldi yl, LOW(com2w_iface)
+  ldi yh, HIGH(com2w_iface)
+  push r15
+    in r15, SREG
+    cli
+    rcall NET_Interface_Periodically         ; (R16)
+    rcall com2wSendNextPkg
+    out SREG, r15
+  pop r15
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wReceiveNextPkg
+;
+; Receive packet.
+;
+; @param Y pointer to start of interface data
+; @clobbers R16, R17, R18, R19, R20, R22, R24, R25, X
+
+com2wReceiveNextPkg:
+;  ldi r20, 3                          ; make sure clock remains low for at least 15us
+;  rcall com2wWaitForClockHighMulti5Us ; (R20, R22)
+;  brcs com2wReceiveNextPkg_end        ; clock got high quite soon, maybe just flaky line
+
+  rcall NET_Buffer_Alloc                          ; R16=buffer num (R16, R17, X)
+  brcs com2wReceiveNextPkg_gotBuffer
+  ldi r16, NET_IFACE_OFFS_ERR_NOBUF_LOW
+  rcall NET_Interface_IncCounter16                ; (R24, R25)
+  rjmp com2wReceiveNextPkg_end
+com2wReceiveNextPkg_gotBuffer:
+  push r16                                        ; buffer number
+    rcall NET_Interface_SetIfaceNumInBuffer       ; (R16, R17)
+    adiw xh:xl, 1
+    ldd r18, Y+NET_IFACE_OFFS_ADDRESS
+    ldi r19, NET_BUFFERS_SIZE-1
+    rcall com2wReceiveAndCheckMsg                 ; (R16, R17, R18, R19, R20, R22, R24, R25)
+  pop r16
+  brcc com2wReceiveNextPkg_relBuffer
+  rcall NET_AddIncomingMsgNum                     ; (R17, R18, X)
+  brcs com2wReceiveNextPkg_end
+
+; debug
+push r18
+  push r19
+    rcall LedSimple_SetFastTiming
+  pop r19
+pop r18
+
+  push r16
+    ldi r16, NET_IFACE_OFFS_ERR_MISSED_LOW
+    rcall NET_Interface_IncCounter16              ; (R24, R25)
+  pop r16
+  ; fall-through to release buffer
+com2wReceiveNextPkg_relBuffer:
+  rcall NET_Buffer_ReleaseByNum                   ; (R16, X)
+com2wReceiveNextPkg_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wReceiveAndCheckMsg
+;
+; Receive a packet into buffer pointed to by X.
+; Expects interrupts to be disabled.
+;
+; @param R18 COM address to listen to
+; @param R19 max buffer size
+; @param X   buffer to receive to
+; @return CFLAG set if msg received, cleared on error
+; @clobbers R16 (R17, R18, R19, R20, R22, R24, R25)
+
+com2wReceiveAndCheckMsg:
+  push xl
+    push xh
+      rcall com2wRecvMsg                     ; (r16, r17, r18, r19, r20, r22, r24, r25, X)
+    pop xh
+  pop xl
+  brcs com2wReceiveAndCheckMsg_recvd
+  ; fall-through, return with CF cleared (from com2wRecvMsg)
+  ret
+com2wReceiveAndCheckMsg_recvd:
+  push xl
+    push xh
+      rcall NETMSG_CheckMessageInBuffer      ; (R16, R17, R18, R19, R20, X)
+    pop xh
+  pop xl
+  brcs com2wReceiveAndCheckMsg_msgOk
+  ldi r16, NET_IFACE_OFFS_ERR_CONTENT_LOW
+  rcall NET_Interface_IncCounter16           ; (R24, R25)
+  clc
+  ret
+com2wReceiveAndCheckMsg_msgOk:
+  ldi r16, NET_IFACE_OFFS_PACKETSIN_LOW
+  rcall NET_Interface_IncCounter16           ; (R24, R25)
+  sec
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wSendNextPkg @global
+;
+; Check whether there is an outgoing message in interface data
+; and send it if possible.
+;
+; @return CFLAG set if okay, clear on error
+; @param Y pointer to start of interface data
+; @clobbers (R16, R17, R18, R20, R22, R24, R25, X)
+
+com2wSendNextPkg:
+  rcall NET_Interface_PeekNextOutgoingMsgNum ; (R17, R18, X)
+  brcc com2wSendNextPkg_end
+  rcall NET_Buffer_Locate                    ; get pointer to buffer (R17)
+  brcc com2wSendNextPkg_end
+  adiw xh:xl, 1                              ; skip buffer header
+  rcall com2wSendMsg                         ; (R16, R18, R20, R22, R24, R25, X)
+  brcc com2wSendNextPkg_end
+  rcall NET_Interface_GetNextOutgoingMsgNum  ; remove from stack (R17, R18, X)
+  rcall NET_Buffer_ReleaseByNum              ; release buffer (R16, X)
+  sec
+com2wSendNextPkg_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wSendMsg
+;
+; @param X pointer to bytes to send
+; @param Y pointer to interface data in SRAM
+; @return CFLAG set if message sent, cleared otherwise
+; @clobbers R16, R18 (R20, R22, R24, R25, X)
+
+com2wSendMsg:
+  ldi r20, 11                           ; wait for about 55us for clock low
+  rcall com2wWaitForClockLowMulti5Us
+  brcs com2wSendMsg_busy                ; CLK got low while waiting, so line is busy
+  push r15
+    in r15, SREG
+    cli                                 ; atomic disable irq and set CLK low
+    rcall com2wDisableClkIrq            ; (none)
+    rcall com2wClkSetLow                ; reserve bus (none)
+    out SREG, r15
+  pop r15
+  adiw xh:xl, NETMSG_OFFS_MSGLEN
+  ld r18, X
+  sbiw xh:xl, NETMSG_OFFS_MSGLEN
+  inc r18                               ; adjust for DESTADDR
+  inc r18                               ; adjust for MSGLEN
+  inc r18                               ; adjust for CRCBYTE
+  rcall com2wWaitTime1                  ; longer wait period (R22)
+  rcall com2wSendBytes                  ; (r16, r17, r18, r22, X)
+  rcall com2wClkSetHigh                 ; make sure bus is released
+  rcall com2wDataSetHigh
+
+  rcall com2wEnableClkIrq               ; (none)
+  ldi r16, NET_IFACE_OFFS_PACKETSOUT_LOW
+  rcall NET_Interface_IncCounter16       ; (R24, R25)
+  sec
+  ret
+com2wSendMsg_busy:
+  ldi r16, NET_IFACE_OFFS_ERR_BUSY_LOW
+  rcall NET_Interface_IncCounter16       ; (R24, R25)
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wSendBytes
+;
+; @param  R18 number of bytes to send
+; @param X pointer to bytes to send
+; @param Y pointer to interface data in SRAM
+; @clobbers: r16, r18, X (r17, r22)
+
+com2wSendBytes:
+com2wSendBytes_loop:
+    rcall com2wClkSetLow                     ; (none)
+    rcall com2wWaitTime1                      ; longer wait period (R22)
+    ld r16, X+
+    rcall com2wSendByte                      ; (R16, R17, R22)
+    dec r18
+  brne com2wSendBytes_loop
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wSendByte
+;
+; @param  R16 byte to send
+; @clobbers: r16, r17 (r22)
+
+com2wSendByte:
+  ldi r17, 8
+com2wSendByte_loop:
+    rcall com2wClkSetLow
+    rcall com2wWaitTime1                        ; longer wait period (R22)
+    lsr r16
+    brcs com2wSendByte_send1
+    rcall com2wDataSetLow
+    rjmp com2wSendByte_sent
+com2wSendByte_send1:
+    rcall com2wDataSetHigh
+com2wSendByte_sent:
+    rcall com2wWaitTime2                        ; shorter wait period (R22)
+    push r15
+      in r15, SREG
+      cli                                       ; ensure time period by disabling irqs
+      rcall com2wClkSetHigh
+      rcall com2wWaitTime1                      ; longer wait period (R22)
+      out SREG, r15
+    pop r15
+    dec r17
+  brne com2wSendByte_loop
+  ret
+; @end
+
+
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wRecvMsg
+;
+; Receive a packet into buffer pointed to by X.
+; Expects interrupts to be disabled.
+;
+; @param R18 COM address to listen to
+; @param R19 max buffer size
+; @param X   buffer to receive to
+; @return CFLAG set if msg received, cleared on error (see R16)
+; @return R16   if CFLAG cleared: 0=message not for this node, otherwise error
+; @clobbers r16, r17, r18, r19, r20, r22, r24, r25, X
+
+com2wRecvMsg:
+  mov r21, r18 ; address
+  ; read destination address
+  rcall com2wRecvByte                    ; (r17, r18, r20, r22)
+  brcc com2wRecvMsg_eIo
+  ; check destination address
+rjmp com2wRecvMsg_forMe ; DEBUG: don't check address
+  cp r16, r21
+  breq com2wRecvMsg_forMe
+  cpi r16, 0xff
+  breq com2wRecvMsg_forMe
+  clr r16
+  rjmp com2wRecvMsg_clcRet
+com2wRecvMsg_forMe:
+  ; store in buffer
+  subi r19, 1
+  brcs com2wRecvMsg_eBadSize
+  st X+, r16
+  
+  ; read remaining msg size
+  rcall com2wRecvByte                    ; (r17, r18, r20, r22)
+  brcc com2wRecvMsg_eIo
+  ; store in buffer
+  subi r19, 1
+  brcs com2wRecvMsg_eBadSize
+  st X+, r16
+  inc r16                                 ; account for CRC byte
+  sub r19, r16
+  brcs com2wRecvMsg_eBadSize
+  mov r19, r16
+com2wRecvMsg_loop:
+    rcall com2wRecvByte                  ; (r17, r18, r20, r22)
+    brcc com2wRecvMsg_eIo
+    st X+, r16
+    dec r19
+  brne com2wRecvMsg_loop
+  sec
+  rjmp com2wRecvMsg_end
+com2wRecvMsg_eBadSize:
+  ldi r16, NET_IFACE_OFFS_ERR_MSGSIZE_LOW
+  rjmp com2wRecvMsg_incCounterRet
+com2wRecvMsg_eIo:
+  ldi r16, NET_IFACE_OFFS_ERR_IO_LOW
+com2wRecvMsg_incCounterRet:
+  rcall NET_Interface_IncCounter16        ; (R24, R25)
+com2wRecvMsg_clcRet:
+  clc
+com2wRecvMsg_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wRecvByte
+;
+; @return CFLAG set if byte received, cleared on error
+; @return r16 byte received
+; @clobbers r17, r18, r20, r22
+
+com2wRecvByte:
+  ldi r17, 8
+  clr r16
+com2wRecvByte_loop:
+    ldi r20, 31                          ; wait up to 155us for clock low
+    rcall com2wWaitForClockLowMulti5Us  ; (R20, R22)
+    brcs com2wRecvByte_waitForClkHigh
+    ldi r20, 31                          ; wait up to 155us for clock low
+    rcall com2wWaitForClockLowMulti5Us  ; (R20, R22)
+    brcc com2wRecvByte_end
+com2wRecvByte_waitForClkHigh:
+    ldi r20, 31                          ; wait up to 155us for clock high
+    rcall com2wWaitForClockHighMulti5Us ; (R20, R22)
+    brcs com2wRecvByte_readBit
+    ldi r20, 31                          ; wait up to 155us for clock high
+    rcall com2wWaitForClockHighMulti5Us ; (R20, R22)
+    brcc com2wRecvByte_end
+
+com2wRecvByte_readBit:
+    ; handle received bit
+    inr r18, COM_DATA_INPUT
+    andi r18, (1<<COM_DATA_PIN)
+    clc
+    breq com2wRecvByte_clockData
+    sec
+com2wRecvByte_clockData:
+    ror r16
+    dec r17
+  brne com2wRecvByte_loop
+  sec
+com2wRecvByte_end:
+  ret
+; @end
+
+
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wEnableClkIrq
+;
+; @clobbers 
+
+com2wEnableClkIrq:
+  push r16
+    inr r16, COM_IRQ_ADDR_CLK
+    sbr r16, (1<<COM_IRQ_BIT_CLK)          ; enable pin change irq for CLK line
+    outr COM_IRQ_ADDR_CLK, r16
+  pop r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wDisableClkIrq
+;
+; @clobbers none
+
+com2wDisableClkIrq:
+  push r16
+    inr r16, COM_IRQ_ADDR_CLK
+    cbr r16, (1<<COM_IRQ_BIT_CLK)        ; disable pin change irq for CLK line
+    outr COM_IRQ_ADDR_CLK, r16
+  pop r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wClkSetHigh
+;
+; @clobbers none
+
+com2wClkSetHigh:
+  cbi COM_CLK_DDR, COM_CLK_PIN           ; set CLK as input
+.ifdef COM_CLK_PUE
+;  cbi COM_CLK_PUE, COM_CLK_PIN           ; disable pullup on CLK
+.else
+  cbi COM_CLK_OUTPUT, COM_CLK_PIN        ; disable pullup on CLK
+.endif
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wClkSetLow
+;
+; @clobbers none
+
+com2wClkSetLow:
+  sbi COM_CLK_DDR, COM_CLK_PIN          ; set CLK as output
+  cbi COM_CLK_OUTPUT, COM_CLK_PIN       ; set CLK low
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wDataSetHigh
+;
+; @clobbers none
+
+com2wDataSetHigh:
+  cbi COM_DATA_DDR, COM_DATA_PIN           ; set DATA as input
+.ifdef COM_DATA_PUE
+;  cbi COM_DATA_PUE, COM_CLK_PIN           ; disable pullup on DATA
+.else
+  cbi COM_DATA_OUTPUT, COM_DATA_PIN        ; disable pullup on DATA
+.endif
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wDataSetLow
+;
+; @clobbers none
+
+com2wDataSetLow:
+  sbi COM_DATA_DDR, COM_DATA_PIN          ; set DATA as output
+  cbi COM_DATA_OUTPUT, COM_DATA_PIN       ; set DATA low
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitForClockHighMulti5Us
+;
+; Wait for high CLK
+;
+; @param  R20 multiple of 5us to wait (e.g. "2" for "10" us, max: 64)
+; @return CFLAG set if okay (state reached), cleared on error
+; @clobbers: r20, r22
+
+com2wWaitForClockHighMulti5Us:
+.if clock == 8000000
+  add r20, r20 ; *2
+  add r20, r20 ; *4
+  add r20, r20 ; *8
+.endif
+.elif clock == 1000000
+; nothing to do
+.else
+  .error "Unhandled clock speed"
+.endif
+
+com2wWaitForClockHighMulti5Us_loop:                   ; 5 cycles per loop
+    sbic COM_CLK_INPUT, COM_CLK_PIN                  ; +2 if skipped, +1 if not
+      rjmp com2wWaitForClockHighMulti5Us_stateReached ; +2
+    dec r20                                            ; +1
+  brne com2wWaitForClockHighMulti5Us_loop             ; +2
+  clc                                                  ; +1
+  ret                                                  ; +4
+com2wWaitForClockHighMulti5Us_stateReached:
+  sec                                                  ; +1
+  ret                                                  ; +4
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitForClockLowMulti5Us
+;
+; Wait for low CLK
+;
+; @param  R20 multiple of 5us to wait (e.g. "2" for "10" us, max: 64)
+; @return CFLAG set if okay (state reached), cleared on error
+; @clobbers: r20, r22
+
+com2wWaitForClockLowMulti5Us:
+.if clock == 8000000
+  add r20, r20 ; *2
+  add r20, r20 ; *4
+  add r20, r20 ; *8
+.endif
+.elif clock == 1000000
+; nothing to do
+.else
+  .error "Unhandled clock speed"
+.endif
+
+com2wWaitForClockLowMulti5Us_loop:                    ; 5 cycles per loop
+    sbis COM_CLK_INPUT, COM_CLK_PIN                  ; +2 if skipped, +1 if not
+      rjmp com2wWaitForClockLowMulti5Us_stateReached  ; +2
+    dec r20                                            ; +1
+  brne com2wWaitForClockLowMulti5Us_loop              ; +2
+  clc                                                  ; +1
+  ret                                                  ; +4
+com2wWaitForClockLowMulti5Us_stateReached:
+  sec                                                  ; +1
+  ret                                                  ; +4
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitTime1
+;
+; waits for longer period (e.g. 30ns)
+;
+; @clobbers R22
+
+com2wWaitTime1:
+  Utils_WaitNanoSecs COM2W_WAITTIME1, 7, r22            ; wait for longer time (minus RCALL and RET)
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitTime2
+;
+; waits for shorter period (e.g. 10ns)
+;
+; @clobbers R22
+
+com2wWaitTime2:
+  Utils_WaitNanoSecs COM2W_WAITTIME2, 7, r22            ; wait for shorter time (minus RCALL and RET)
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wPcintIsr @global @isr
+;
+; ISR for PCINT0/1
+;
+; @clobbers: none
+
+com2wPcintIsr:
+  push r15
+    in r15, SREG
+    sbic COM_CLK_INPUT, COM_CLK_PIN
+      rjmp com2wPcintIsr_end
+    ; low, read packet
+    push r16
+      push r17
+        push r18
+          push r19
+            push r20
+              push r21
+                push r22
+                  push r24
+                    push r25
+                      push xl
+                        push xh
+                          push yl
+                            push yh
+                              ldi yl, LOW(com2w_iface)
+                              ldi yh, HIGH(com2w_iface)
+                              rcall com2wReceiveNextPkg         ; (R16, R17, R18, R19, R20, R21, R22, R24, R25, X)
+                            pop yh
+                          pop yl
+                        pop xh
+                      pop xl
+                    pop r25
+                  pop r24
+                pop r22
+              pop r21
+            pop r20
+          pop r19
+        pop r18
+      pop r17
+    pop r16
+com2wPcintIsr_end:
+    out SREG, r15
+  pop r15
+  reti
+; @end
+
+
+
+#endif ; AVR_MODULES_COM2W_COM2W_H
+
diff --git a/avr/modules/com2w/com2w1.asm b/avr/modules/com2w/com2w1.asm
new file mode 100644
index 0000000..73ed414
--- /dev/null
+++ b/avr/modules/com2w/com2w1.asm
@@ -0,0 +1,638 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+#ifndef AVR_MODULES_COM2W_COM2W1_H
+#define AVR_MODULES_COM2W_COM2W1_H
+
+
+.dseg
+
+com2w1_iface: .byte COM2W_IFACE_SIZE
+
+
+
+.cseg
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W1_Init
+;
+; @clobbers 
+
+COM2W1_Init:
+  ldi yl, LOW(com2w1_iface)
+  ldi yh, HIGH(com2w1_iface)
+  rcall NET_Interface_Init                 ; (R16, R17, X)
+  ldi r16, COM2W_MODE_IDLE
+  rcall com2wSetMode                       ; (R17)
+
+  ; setup CLK line (as input, disable internal pull-up resistor)
+  cbi COM_CLK1_DDR, COM_CLK1_PIN           ; set CLK as input
+.ifdef COM_CLK1_PUE
+  inr r16, COM_CLK1_PUE
+  cbr r16, (1<<COM_CLK1_PIN)               ; disable pullup on CLK
+  outr COM_CLK1_PUE, r16
+.else
+  cbi COM_CLK1_OUTPUT, COM_CLK1_PIN        ; disable pullup on CLK
+.endif
+
+  ; setup DATA line (as input, disable internal pull-up resistor)
+  cbi COM_DATA1_DDR, COM_DATA1_PIN         ; set DATA as input
+.ifdef COM_DATA1_PUE
+  inr r16, COM_DATA1_PUE
+  cbr r16, (1<<COM_DATA1_PIN)              ; disable pullup on DATA
+  outr COM_DATA1_PUE, r16
+.else
+  cbi COM_DATA1_OUTPUT, COM_DATA1_PIN      ; disable pullup on DATA
+.endif
+
+  ; setup pin-change interrupt for CLK
+  rcall com2w1EnableClkIrq
+
+  inr r16, COM_IRQ_ADDR_CLK1
+  sbr r16, (1<<COM_IRQ_BIT_CLK1)           ; enable pin change irq for ATTN line
+  outr COM_IRQ_ADDR_CLK1, r16
+
+  inr r16, GIMSK                           ; enable pin change irq PCIE0 or PCIE1
+  sbr r16, (1<<COM_IRQ_GIMSK_CLK1)
+  outr GIMSK, r16
+  ldi r16, (1<<COM_IRQ_GIFR_CLK1)          ; clear pending irq by writing 1 to ATTN bit
+  outr GIFR, r16
+
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W1_Periodically @global
+;
+; @clobbers R16, Y
+
+COM2W1_Periodically:
+  ldi yl, LOW(com2w1_iface)
+  ldi yh, HIGH(com2w1_iface)
+  rcall com2wPeriodically
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1EnableClkIrq
+;
+; @clobbers 
+
+com2w1EnableClkIrq:
+  push r16
+    inr r16, COM_IRQ_ADDR_CLK1
+    sbr r16, (1<<COM_IRQ_BIT_CLK1)          ; enable pin change irq for CLK line
+    outr COM_IRQ_ADDR_CLK1, r16
+  pop r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1DisableClkIrq
+;
+; @clobbers none
+
+com2w1DisableClkIrq:
+  push r16
+    inr r16, COM_IRQ_ADDR_CLK1
+    cbr r16, (1<<COM_IRQ_BIT_CLK1)        ; disable pin change irq for CLK line
+    outr COM_IRQ_ADDR_CLK1, r16
+  pop r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1ClkSetHigh
+;
+; @clobbers none
+
+com2w1ClkSetHigh:
+  cbi COM_CLK1_DDR, COM_CLK1_PIN           ; set CLK as input
+.ifdef COM_CLK1_PUE
+;  cbi COM_CLK1_PUE, COM_CLK1_PIN           ; disable pullup on CLK
+.else
+  cbi COM_CLK1_OUTPUT, COM_CLK1_PIN        ; disable pullup on CLK
+.endif
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1ClkSetLow
+;
+; @clobbers none
+
+com2w1ClkSetLow:
+  sbi COM_CLK1_DDR, COM_CLK1_PIN          ; set CLK as output
+  cbi COM_CLK1_OUTPUT, COM_CLK1_PIN       ; set CLK low
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1DataSetHigh
+;
+; @clobbers none
+
+com2w1DataSetHigh:
+  cbi COM_DATA1_DDR, COM_DATA1_PIN           ; set DATA as input
+.ifdef COM_DATA1_PUE
+;  cbi COM_DATA1_PUE, COM_CLK1_PIN           ; disable pullup on DATA
+.else
+  cbi COM_DATA1_OUTPUT, COM_DATA1_PIN        ; disable pullup on DATA
+.endif
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1DataSetLow
+;
+; @clobbers none
+
+com2w1DataSetLow:
+  sbi COM_DATA1_DDR, COM_DATA1_PIN          ; set DATA as output
+  cbi COM_DATA1_OUTPUT, COM_DATA1_PIN       ; set DATA low
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1ReadNextBit
+;
+; @clobbers r16, r17, r18, r20, r22
+
+com2w1ReadNextBit:
+  ldi r20, 50                           ; wait for up to 250us for clock rise
+  rcall com2w1WaitForClockHighMulti5Us  ; (R20, R22)
+  brcc com2w1ReadNextBit_end
+  ; clock is high now, read bit
+  inr r17, COM_DATA1_INPUT
+  ; reset read timer (for leaving skipping mode)
+  clr r16
+  std Y+NET_IFACE_OFFS_READTIMER, r16
+  ; check mode
+  ldd r16, Y+COM2W_IFACE_OFFS_MODE
+  cpi r16, COM2W_MODE_READING
+  brne com2w1ReadNextBit_end
+  ; handle received bit
+  ldd r16, Y+COM2W_IFACE_OFFS_CURRBYTE
+  ldd r18, Y+COM2W_IFACE_OFFS_BITCOUNTER
+  andi r17, (1<<COM_DATA1_PIN)
+  clc
+  breq com2w1ReadNextBit_clockData
+  sec
+com2w1ReadNextBit_clockData:
+  ror r16
+  std Y+COM2W_IFACE_OFFS_CURRBYTE, r16
+  inc r18                                ; bit counter
+  std Y+COM2W_IFACE_OFFS_BITCOUNTER, r18
+  cpi r18, 8
+  brne com2w1ReadNextBit_end
+  ; write byte into buffer
+  push xl
+    push xh
+      rcall com2wByteRecvd               ; (r16, r17, r18, X)
+    pop xh
+  pop xl
+  ; prepare for next byte
+  clr r16
+  std Y+COM2W_IFACE_OFFS_BITCOUNTER, r16
+  std Y+COM2W_IFACE_OFFS_CURRBYTE, r16
+com2w1ReadNextBit_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1WaitForClockHighMulti5Us
+;
+; Wait for high CLK
+;
+; @param  R20 multiple of 5us to wait (e.g. "2" for "10" us, max: 64)
+; @return CFLAG set if okay (state reached), cleared on error
+; @clobbers: r20, r22
+
+com2w1WaitForClockHighMulti5Us:
+.if clock == 8000000
+  add r20, r20 ; *2
+  add r20, r20 ; *4
+  add r20, r20 ; *8
+.endif
+.elif clock == 1000000
+; nothing to do
+.else
+  .error "Unhandled clock speed"
+.endif
+
+com2w1WaitForClockHighMulti5Us_loop:                   ; 5 cycles per loop
+    sbic COM_CLK1_INPUT, COM_CLK1_PIN                  ; +2 if skipped, +1 if not
+      rjmp com2w1WaitForClockHighMulti5Us_stateReached ; +2
+    dec r20                                            ; +1
+  brne com2w1WaitForClockHighMulti5Us_loop             ; +2
+  clc                                                  ; +1
+  ret                                                  ; +4
+com2w1WaitForClockHighMulti5Us_stateReached:
+  sec                                                  ; +1
+  ret                                                  ; +4
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1WaitForClockLowMulti5Us
+;
+; Wait for low CLK
+;
+; @param  R20 multiple of 5us to wait (e.g. "2" for "10" us, max: 64)
+; @return CFLAG set if okay (state reached), cleared on error
+; @clobbers: r20, r22
+
+com2w1WaitForClockLowMulti5Us:
+.if clock == 8000000
+  add r20, r20 ; *2
+  add r20, r20 ; *4
+  add r20, r20 ; *8
+.endif
+.elif clock == 1000000
+; nothing to do
+.else
+  .error "Unhandled clock speed"
+.endif
+
+com2w1WaitForClockLowMulti5Us_loop:                    ; 5 cycles per loop
+    sbis COM_CLK1_INPUT, COM_CLK1_PIN                  ; +2 if skipped, +1 if not
+      rjmp com2w1WaitForClockLowMulti5Us_stateReached  ; +2
+    dec r20                                            ; +1
+  brne com2w1WaitForClockLowMulti5Us_loop              ; +2
+  clc                                                  ; +1
+  ret                                                  ; +4
+com2w1WaitForClockLowMulti5Us_stateReached:
+  sec                                                  ; +1
+  ret                                                  ; +4
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1SendMsg
+;
+; @param X pointer to bytes to send
+; @param Y pointer to interface data in SRAM
+; @return CFLAG set if message sent, cleared otherwise
+; @clobbers R16, R18 (R20, R22, R24, R25, X)
+
+com2w1SendMsg:
+  ldi r20, 11                            ; wait for about 55us for clock low
+  rcall com2w1WaitForClockLowMulti5Us
+  brcs com2w1SendMsg_busy                ; CLK got low while waiting, so line is busy
+  push r15
+    in r15, SREG
+    cli                                  ; atomic disable irq and set CLK low
+    rcall com2w1DisableClkIrq            ; (none)
+    rcall com2w1ClkSetLow                ; reserve bus (none)
+    out SREG, r15
+  pop r15
+  adiw xh:xl, NETMSG_OFFS_MSGLEN
+  ld r18, X
+  sbiw xh:xl, NETMSG_OFFS_MSGLEN
+  inc r18                                ; adjust for DESTADDR
+  inc r18                                ; adjust for MSGLEN
+  inc r18                                ; adjust for CRCBYTE
+  rcall com2wWaitTime1                   ; longer wait period (R22)
+  rcall com2w1SendBytes                  ; (r16, r17, r18, r22, X)
+  rcall com2w1ClkSetHigh                 ; make sure bus is released
+  rcall com2w1DataSetHigh
+
+  rcall com2w1EnableClkIrq               ; (none)
+  ldi r16, NET_IFACE_OFFS_PACKETSOUT_LOW
+  rcall NET_Interface_IncCounter16       ; (R24, R25)
+  sec
+  ret
+com2w1SendMsg_busy:
+  ldi r16, NET_IFACE_OFFS_ERR_BUSY_LOW
+  rcall NET_Interface_IncCounter16       ; (R24, R25)
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1SendBytes
+;
+; @param  R18 number of bytes to send
+; @param X pointer to bytes to send
+; @param Y pointer to interface data in SRAM
+; @clobbers: r16, r18, X (r17, r22)
+
+com2w1SendBytes:
+com2w1SendBytes_loop:
+    rcall com2w1ClkSetLow                     ; (none)
+    rcall com2wWaitTime1                      ; longer wait period (R22)
+    ld r16, X+
+    rcall com2w1SendByte                      ; (R16, R17, R22)
+    dec r18
+  brne com2w1SendBytes_loop
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1SendByte
+;
+; @param  R16 byte to send
+; @clobbers: r16, r17 (r22)
+
+com2w1SendByte:
+  ldi r17, 8
+com2w1SendByte_loop:
+    rcall com2w1ClkSetLow
+    rcall com2wWaitTime1                        ; longer wait period (R22)
+    lsr r16
+    brcs com2w1SendByte_send1
+    rcall com2w1DataSetLow
+    rjmp com2w1SendByte_sent
+com2w1SendByte_send1:
+    rcall com2w1DataSetHigh
+com2w1SendByte_sent:
+    rcall com2wWaitTime2                        ; shorter wait period (R22)
+    push r15
+      in r15, SREG
+      cli                                       ; ensure time period by disabling irqs
+      rcall com2w1ClkSetHigh
+      rcall com2wWaitTime1                      ; longer wait period (R22)
+      out SREG, r15
+    pop r15
+    dec r17
+  brne com2w1SendByte_loop
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W1_Run @global
+;
+; @return CFLAG set if something done, cleared otherwise
+; @clobbers all
+
+COM2W1_Run:
+  ldi yl, LOW(com2w1_iface)
+  ldi yh, HIGH(com2w1_iface)
+  rjmp com2w1RunMode          ; (all but Y)
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1RunMode
+;
+; @clobbers all
+
+com2w1RunMode:
+  cpi r16, COM2W_MODE_NUM
+  brcs COM2W1_Run_jump
+  ldi r16, COM2W_MODE_IDLE              ; unknown mode, set to idle
+  rcall com2wSetMode                    ; (R17)
+  sec
+  ret
+COM2W1_Run_jump:
+  ldi zl, LOW(com2w1ModeJumpTable)
+  ldi zh, HIGH(com2w1ModeJumpTable)
+  add zl, r16
+  adc zh, r16
+  sub zh, r16
+  ijmp
+com2w1ModeJumpTable:
+  rjmp com2w1RunIdle
+  rjmp com2w1RunReading
+  rjmp com2w1RunSkipping
+  rjmp com2w1RunWriting
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1RunIdle
+;
+; @param Y pointer to interface data in SRAM
+; @clobbers R16, R17, R22, R24, R25, X
+
+com2w1RunIdle:
+rjmp com2w1RunIdle_end ; DEBUG
+  push r15
+    in r15, SREG
+    cli
+    ; look for outbound message
+    rcall NET_Interface_PeekNextOutgoingMsgNum ; r16=msgNum
+    brcs com2w1RunIdle_haveMsg
+    out SREG, r15
+  pop r15
+  clc
+  rjmp com2w1RunIdle_end
+
+com2w1RunIdle_haveMsg:
+    mov r24, r16
+    ldi r16, COM2W_MODE_WRITING
+    rcall com2wSetMode                         ; (R17)
+    mov r16, r24
+    out SREG, r15
+  pop r15
+
+  push r16
+    rcall NET_Buffer_Locate                    ; (R17)
+    adiw xh:xl, 1
+    rcall com2w1SendMsg                        ; (R16, R17, R22, R24, R25, X)
+    push r15                           
+      inr r15, SREG                            ; save SREG (no CLI, we want to save CFLAG only)
+      ldi r16, COM2W_MODE_IDLE
+      rcall com2wSetMode                       ; (R17)
+      out SREG, r15                            ; restore SREG
+    pop r15
+  pop r16
+  brcc com2w1RunIdle_end
+
+  push r15
+    in r15, SREG
+    cli
+    rcall NET_Interface_GetNextOutgoingMsgNum  ; take current msg off the queue
+    rcall NET_Buffer_ReleaseByNum              ; (R16, X)
+    out SREG, r15
+  pop r15
+  sec
+com2w1RunIdle_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1RunReading
+;
+; @param Y pointer to interface data in SRAM
+; @clobbers none
+
+com2w1RunReading:
+  ; check for timeout (Y+NET_IFACE_OFFS_READTIMER)
+  ldd r16, Y+NET_IFACE_OFFS_READTIMER
+  cpi r16, COM2W_READING_MAXREADCOUNTER
+  brcc com2w1RunReading_goIdle
+  ldd r16, Y+COM2W_IFACE_OFFS_MODECOUNTER
+  cpi r16, COM2W_READING_MAXMODECOUNTER
+  brcc com2w1RunReading_goIdle
+  clc
+  rjmp com2w1RunReading_end
+com2w1RunReading_goIdle:
+  ldi r16, NET_IFACE_OFFS_ERR_IO_LOW
+  rcall NET_Interface_IncCounter16     ; (R24, R25)
+  ldi r16, COM2W_MODE_IDLE
+  rcall com2wSetMode                   ; (r17)
+  sec
+com2w1RunReading_end:
+  ret
+; @end
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1RunSkipping
+;
+; @param Y pointer to interface data in SRAM
+; @clobbers r16 (r17)
+
+com2w1RunSkipping:
+  ; check for timeout (Y+NET_IFACE_OFFS_READTIMER)
+  ldd r16, Y+NET_IFACE_OFFS_READTIMER
+  cpi r16, COM2W_SKIPPING_MAXREADCOUNTER
+  brcc com2w1RunSkipping_goIdle
+  ldd r16, Y+COM2W_IFACE_OFFS_MODECOUNTER
+  cpi r16, COM2W_SKIPPING_MAXMODECOUNTER
+  brcc com2w1RunSkipping_goIdle
+  clc
+  rjmp com2w1RunSkipping_end
+com2w1RunSkipping_goIdle:
+  ldi r16, COM2W_MODE_IDLE
+  rcall com2wSetMode                   ; (r17)
+  sec
+com2w1RunSkipping_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1RunWriting
+;
+; @param Y pointer to interface data in SRAM
+; @clobbers none
+
+com2w1RunWriting:
+  ; TODO: check for timeout
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W1_ClkChangeIsr @global @isr
+;
+; @clobbers none
+
+COM2W1_ClkChangeIsr:
+  push r15
+    in r15, SREG
+    push r16
+      inr r16, COM_CLK1_INPUT                ; read clk state early
+      rcall COM2W1_HandleClockInterrupt
+    pop r16
+    out SREG, r15
+  pop r15
+  reti
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine COM2W1_HandleClockInterrupt @global
+;
+; @param r16 data from COM_CLKn_INPUT
+; @clobbers none
+
+COM2W1_HandleClockInterrupt:
+  push r16
+    push r17
+      push r18
+        push xl
+          push xh
+            push yl
+              push yh
+                ldi yl, LOW(com2w1_iface)
+                ldi yh, HIGH(com2w1_iface)
+                rcall com2w1ActOnClock       ; (r16, r17, r18, X)
+              pop yh
+            pop yl
+          pop xh
+        pop xl
+      pop r18
+    pop r17
+  pop r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w1ActOnClock
+;
+; @param r16 data from COM_CLKn_INPUT
+; @clobbers r16 (r17, r18, X)
+
+com2w1ActOnClock:
+  andi r16, (1<<COM_CLK1_PIN)
+  brne com2w1ActOnClock_end
+  ldd r17, Y+COM2W_IFACE_OFFS_MODE
+  cpi r17, COM2W_MODE_READING
+  breq com2w1ActOnClock_readBit
+  cpi r17, COM2W_MODE_IDLE
+  brne com2w1ActOnClock_end
+  rcall com2wStartReading           ; (r16, r17, X)
+com2w1ActOnClock_readBit:
+  push r20
+    push r22
+      rcall com2w1ReadNextBit            ; (r16, r17, r18, r20, r22)
+    pop r22
+  pop r20
+com2w1ActOnClock_end:
+  ret
+; @end
+
+
+
+
+
+#endif ; AVR_MODULES_COM2W_COM2W1_H
+
diff --git a/avr/modules/com2w/common.asm b/avr/modules/com2w/common.asm
new file mode 100644
index 0000000..7576912
--- /dev/null
+++ b/avr/modules/com2w/common.asm
@@ -0,0 +1,244 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+#ifndef AVR_MODULES_COM2W_COMMON_H
+#define AVR_MODULES_COM2W_COMMON_H
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wPeriodically @global
+;
+; @clobbers R16, Y
+
+com2wPeriodically:
+  push r15
+    in r15, SREG
+    cli
+    rcall NET_Interface_Periodically
+    ldd r16, Y+COM2W_IFACE_OFFS_MODECOUNTER
+    inc r16
+    breq com2wPeriodically_end
+    std Y+COM2W_IFACE_OFFS_MODECOUNTER, r16
+com2wPeriodically_end:
+    out SREG, r15
+  pop r15
+  ret
+; @end
+
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wSetMode
+;
+; Doesn't change processor status flags!
+;
+; @param R16 mode
+; @clobbers R17
+
+com2wSetMode:
+  push r15
+    in r15, SREG
+    cli
+    ldd r17, Y+COM2W_IFACE_OFFS_MODE
+    cp r16, r17
+    breq com2wSetMode_end
+    std Y+COM2W_IFACE_OFFS_MODE, r16
+    clr r17
+    std Y+COM2W_IFACE_OFFS_MODECOUNTER, r17
+com2wSetMode_end:
+    out SREG, r15
+  pop r15
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wStartReading
+;
+; @param Y pointer to interface data in SRAM
+; @clobbers R16, R17, X
+
+com2wStartReading:
+  mov xl, yl
+  mov xh, yh
+  adiw xh:xl, COM2W_IFACE_OFFS_BUFFER
+  std Y+COM2W_IFACE_OFFS_BUFPOS_LOW, xl
+  std Y+COM2W_IFACE_OFFS_BUFPOS_HIGH, xh
+  ldi r16, COM2W_BUFFER_SIZE
+  std Y+COM2W_IFACE_OFFS_BUFLEFT, r16
+  clr r16
+  std Y+COM2W_IFACE_OFFS_BUFUSED, r16
+  ldi r16, COM2W_MODE_READING
+  rcall com2wSetMode                      ; (R17)
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wByteRecvd
+;
+; @param r16 byte received
+; @param Y   pointer to interface data
+; @return CFLAG set if okay, cleared on error
+; @clobbers r16, r17, r18, X
+
+com2wByteRecvd:
+  ldd xl, Y+COM2W_IFACE_OFFS_BUFPOS_LOW
+  ldd xh, Y+COM2W_IFACE_OFFS_BUFPOS_HIGH
+  ldd r17, Y+COM2W_IFACE_OFFS_BUFLEFT
+  ldd r18, Y+COM2W_IFACE_OFFS_BUFUSED
+  tst r17
+  breq com2wByteRecvd_overflow
+  st X+, r16
+  std Y+COM2W_IFACE_OFFS_BUFPOS_LOW, xl
+  std Y+COM2W_IFACE_OFFS_BUFPOS_HIGH, xh
+  inc r18
+  std Y+COM2W_IFACE_OFFS_BUFUSED, r18
+  dec r17
+  std Y+COM2W_IFACE_OFFS_BUFLEFT, r17
+  breq com2wByteRecvd_msgComplete
+  cpi r18, 2
+  sec
+  brne com2wByteRecvd_end
+
+  ; determine msg size
+  inc r16                                       ; last byte was payload length, add byte for crc
+  cp r17, r16                                   ; compare remaining length against remaining space
+  brcs com2wByteRecvd_eMsgSize
+  std Y+COM2W_IFACE_OFFS_BUFLEFT, r16
+  tst r16
+  sec
+  brne com2wByteRecvd_end
+com2wByteRecvd_msgComplete:
+  push r19                                      ; pushing these registers is now only needed *here* for every
+    push r20                                    ; message received. Otherwise they would have been pushed
+      push r24                                  ; on every bit adding much more execution time to the
+        push r25                                ; irq service routine
+          push zl
+            push zh
+              rcall com2wMsgReceived            ; (R16, R17, R18, R19, R20, R24, R25, X, Z)
+            pop zh
+          pop zl
+        pop r25
+      pop r24
+    pop r20
+  pop r19
+  rjmp com2wByteRecvd_end
+com2wByteRecvd_overflow:
+  ldi r16, NET_IFACE_OFFS_ERR_MISSED_LOW
+  rjmp com2wByteRecvd_error
+com2wByteRecvd_eMsgSize:
+
+  ldi r16, NET_IFACE_OFFS_ERR_MSGSIZE_LOW
+com2wByteRecvd_error:
+  push r24
+    push r25
+      rcall NET_Interface_IncCounter16          ; (R24, R25)
+    pop r25
+  pop r24
+  ldi r16, COM2W_MODE_SKIPPING                  ; error, enter skipping mode
+  rcall com2wSetMode
+  clc
+com2wByteRecvd_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wMsgReceived
+;
+; @param Y pointer to interface data in SRAM
+; @return CFLAG set if okay, cleared on error
+; @clobbers R16, R17, R18, X, Z (R19, R20, R24, R25)
+
+com2wMsgReceived:
+  mov xl, yl
+  mov xh, yh
+  adiw xh:xl, COM2W_IFACE_OFFS_BUFFER
+  mov zl, xl                                 ; Z=buffer in IFACE
+  mov zh, xh
+  rcall NETMSG_CheckMessageInBuffer          ; (R16, R17, R18, R19, R20, X)
+  brcc com2wMsgReceived_econtent
+  ; msg valid, alloc buffer
+  rcall NET_Buffer_Alloc                     ; X=buffer, R16=bufnum (R16, R17, X)
+  brcc com2wMsgReceived_enobuf
+  mov r18, r16                               ; buffer num
+  rcall NET_Interface_SetIfaceNumInBuffer    ; (R16, R17)
+  adiw xh:xl, 1                              ; skip buffer header
+  ldd r17, Y+COM2W_IFACE_OFFS_BUFUSED        ; always is at least 2 here
+com2wMsgReceived_copyLoop:
+    ld r16, Z+
+    st X+, r16
+    dec r17
+  brne com2wMsgReceived_copyLoop
+  mov r16, r18                               ; buffer num
+  rcall NET_AddIncomingMsgNum                ; (R17, R18, X)
+  brcc com2wMsgReceived_enoadd
+  ldi r16, NET_IFACE_OFFS_PACKETSIN_LOW
+  rcall NET_Interface_IncCounter16           ; (R24, R25)
+  sec
+  rjmp com2wMsgReceived_setIdleAndEnd
+com2wMsgReceived_enoadd:
+  rcall NET_Buffer_ReleaseByNum
+  rjmp com2wMsgReceived_enobuf
+com2wMsgReceived_enobuf:
+  ldi r16, NET_IFACE_OFFS_ERR_NOBUF_LOW
+  rjmp com2wMsgReceived_err
+com2wMsgReceived_econtent:
+  ldi r16, NET_IFACE_OFFS_ERR_CONTENT_LOW
+com2wMsgReceived_err:
+  rcall NET_Interface_IncCounter16           ; (R24, R25)
+  clc
+com2wMsgReceived_setIdleAndEnd:
+  ldi r16, COM2W_MODE_IDLE
+  rcall com2wSetMode                         ; (R17, doesn't change CFLAG!)
+com2wMsgReceived_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitTime1
+;
+; waits for longer period (e.g. 30ns)
+;
+; @clobbers R22
+
+com2wWaitTime1:
+  Utils_WaitNanoSecs COM2W_WAITTIME1, 7, r22            ; wait for longer time (minus RCALL and RET)
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2wWaitTime2
+;
+; waits for shorter period (e.g. 10ns)
+;
+; @clobbers R22
+
+com2wWaitTime2:
+  Utils_WaitNanoSecs COM2W_WAITTIME2, 7, r22            ; wait for shorter time (minus RCALL and RET)
+  ret
+; @end
+
+
+
+
+#endif ; AVR_MODULES_COM2W_COMMON_H
+
diff --git a/avr/modules/com2w/defs.asm b/avr/modules/com2w/defs.asm
new file mode 100644
index 0000000..0fd5c39
--- /dev/null
+++ b/avr/modules/com2w/defs.asm
@@ -0,0 +1,74 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+#ifndef AVR_MODULES_COM2W_DEFS_H
+#define AVR_MODULES_COM2W_DEFS_H
+
+
+.equ COM2W_WAITTIME1 = 30000
+.equ COM2W_WAITTIME2 = 10000
+
+.equ COM2W_SKIPPING_MAXREADCOUNTER = 1
+.equ COM2W_SKIPPING_MAXMODECOUNTER = 20  ; stay max 2s in skipping mode
+
+.equ COM2W_READING_MAXREADCOUNTER  = 1
+.equ COM2W_READING_MAXMODECOUNTER  = 20  ; stay max 2s in reading mode
+
+
+;
+; .equ COM2W_DATA0_DDR     = DDRA
+; .equ COM2W_DATA0_INPUT   = PINA
+; .equ COM2W_DATA0_OUTPUT  = PORTA
+; .equ COM2W_DATA0_PUE     = PUEA
+; .equ COM2W_DATA0_PIN     = PORTA2
+;
+; .equ COM2W_CLK0_DDR      = DDRA
+; .equ COM2W_CLK0_INPUT    = PINA
+; .equ COM2W_CLK0_OUTPUT   = PORTA
+; .equ COM2W_CLK0_PUE      = PUEA
+; .equ COM2W_CLK0_PIN      = PORTA0
+
+; .equ COM2W_IRQ_ADDR_CLK0  = PCMSK0
+; .equ COM2W_IRQ_BIT_CLK0   = PCINT0        ; bit 0 in PCMSK0
+; .equ COM2W_IRQ_GIFR_CLK0  = PCIF0
+; .equ COM2W_IRQ_GIMSK_CLK0 = PCIE0
+
+
+
+
+.equ COM2W_BUFFER_SIZE = NET_BUFFERS_SIZE-1
+
+
+
+.equ COM2W_MODE_IDLE            = 0
+.equ COM2W_MODE_READING         = 1
+.equ COM2W_MODE_SKIPPING        = 2
+.equ COM2W_MODE_WRITING         = 3
+.equ COM2W_MODE_NUM             = 4
+
+
+.equ COM2W_IFACE_OFFS_BEGIN        = NET_IFACE_SIZE
+.equ COM2W_IFACE_OFFS_CURRBYTE     = COM2W_IFACE_OFFS_BEGIN
+.equ COM2W_IFACE_OFFS_BITCOUNTER   = COM2W_IFACE_OFFS_BEGIN+1
+.equ COM2W_IFACE_OFFS_MODE         = COM2W_IFACE_OFFS_BEGIN+2
+.equ COM2W_IFACE_OFFS_MODECOUNTER  = COM2W_IFACE_OFFS_BEGIN+3
+.equ COM2W_IFACE_OFFS_BUFPOS_LOW   = COM2W_IFACE_OFFS_BEGIN+4
+.equ COM2W_IFACE_OFFS_BUFPOS_HIGH  = COM2W_IFACE_OFFS_BEGIN+5
+.equ COM2W_IFACE_OFFS_BUFUSED      = COM2W_IFACE_OFFS_BEGIN+6
+.equ COM2W_IFACE_OFFS_BUFLEFT      = COM2W_IFACE_OFFS_BEGIN+7
+.equ COM2W_IFACE_OFFS_BUFFER       = COM2W_IFACE_OFFS_BEGIN+8
+
+.equ COM2W_IFACE_SIZE              = COM2W_IFACE_OFFS_BUFFER+COM2W_BUFFER_SIZE
+
+
+
+
+#endif ; AVR_MODULES_COM2W_DEFS_H
+
+