diff --git a/avr/modules/uart_bitbang/0BUILD b/avr/modules/uart_bitbang/0BUILD
new file mode 100644
index 0000000..ac289d9
--- /dev/null
+++ b/avr/modules/uart_bitbang/0BUILD
@@ -0,0 +1,12 @@
+<?xml?>
+
+<gwbuild>
+
+  <extradist>
+    main.asm
+    bytelevel.asm
+  </extradist>
+
+</gwbuild>
+
+
diff --git a/avr/modules/uart_bitbang/bytelevel.asm b/avr/modules/uart_bitbang/bytelevel.asm
new file mode 100644
index 0000000..caf5ffa
--- /dev/null
+++ b/avr/modules/uart_bitbang/bytelevel.asm
@@ -0,0 +1,186 @@
+; ***************************************************************************
+; copyright   : (C) 2024 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.   *
+; ***************************************************************************
+
+
+
+; ---------------------------------------------------------------------------
+; @macro UART_BB_M_WAIT_FOR_PIN_LOW IN_REG_DATA, IN_PINNUM
+;                                 0            1
+; Wait for a pin to become low
+; @param %0 DATA register for input pin (e.g. PINB)
+; @param %1 pin number for input (e.g. PORTB1)
+; @return CFLAG set if okay, clear otherwise
+; @clobbers R17, R22
+
+.macro UART_BB_M_WAIT_FOR_PIN_LOW
+  ldi r17, 200
+l_loop:
+    sbis @0, @1
+      rjmp l_reached
+    Utils_WaitNanoSecs 5000, 0, r22                ; wait for 5us
+    dec r17
+  brne l_loop
+  clc
+  rjmp l_end
+l_reached:
+  sec
+l_end:
+.endmacro
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @macro UART_BB_M_WAIT_FOR_PIN_HIGH IN_REG_DATA, IN_PINNUM
+;                                 0            1
+; Wait for a pin to become high
+; @param %0 DATA register for input pin (e.g. PINB)
+; @param %1 pin number for input (e.g. PORTB1)
+; @return CFLAG set if okay, clear otherwise
+; @clobbers R17, R22
+
+.macro UART_BB_M_WAIT_FOR_PIN_HIGH
+  ldi r17, 200
+l_loop:
+    sbic @0, @1
+      rjmp l_reached
+    Utils_WaitNanoSecs 5000, 0, r22                ; wait for 5us
+    dec r17
+  brne l_loop
+  clc
+  rjmp l_end
+l_reached:
+  sec
+l_end:
+.endmacro
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_SendByte
+;
+; Send a byte.
+; We only set the data pin to low at the beginning for the startbit. After that
+; we only change the pin direction (e.g. input vs output):
+; - for 0 bit: set DDR to output, forcing the data line low
+; - for 1 bit: set DDR to input, letting the external pullup R pull the data line to HIGH
+;              since the output pin is still set to 0 the internal pullup is disabled
+; Expects interrupts to be disabled.
+;
+; @param R16 byte to send
+; @return CFLAG set if okay, clear otherwise
+; @clobbers R16, R21, R22
+
+uartBitbang_SendByte:
+  ldi r21, 8                                       ; +1 bits left
+  ; send startbit
+  cbi COM_TXD_DATA, COM_TXD_PIN                    ; +2 set DATA low
+  sbi COM_TXD_DDR, COM_TXD_PIN                     ; +2 set DATA as output
+  Utils_WaitNanoSecs COM_BIT_LENGTH, 1, r22        ; wait for one bit duration
+  ; send data bits
+uartBitbang_SendByte_loop:                         ; 9 for low bit
+    lsr r16                                        ; 1+ bit to send -> CARRY
+    brcs uartBitbang_SendByte_setHigh              ; HI: +2, LO: +1
+uartBitbang_SendByte_setLow:
+    sbi COM_TXD_DDR, COM_TXD_PIN                   ; +2 set DATA as output
+    Utils_WaitNanoSecs COM_BIT_LENGTH, 9, r22
+    rjmp uartBitbang_SendByte_loopEnd              ; +2
+uartBitbang_SendByte_setHigh:
+    cbi COM_TXD_DDR, COM_TXD_PIN                   ; +2 set DATA as input, pullup R makes it ONE
+    nop                                            ; +1 (to make pin change available)
+    Utils_WaitNanoSecs COM_HALFBIT_LENGTH, 0, r22  ; wait for half a bit length for line to safely settle
+    sbis COM_RXD_DATA, COM_RXD_PIN                 ; +1 if no skip, +2 if skipped
+      rjmp uartBitbang_SendByte_error              ; +2 if error (collision: we wanted line to be high but it is low)
+    Utils_WaitNanoSecs COM_HALFBIT_LENGTH, 11, r22
+uartBitbang_SendByte_loopEnd:
+    dec r21                                        ; +1
+  brne uartBitbang_SendByte_loop                   ; +2, sum per loop: 10 cycles
+  ; send stopbit
+  cbi COM_TXD_DDR, COM_TXD_PIN                     ; +2 set DATA as input, pullup R makes it ONE
+  Utils_WaitNanoSecs COM_BIT_LENGTH, 0, r22        ; wait for one bit length
+  sec
+  ret
+
+uartBitbang_SendByte_error:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbangReceiveByte
+;
+; Read a byte.
+; Expects interrupts to be disabled.
+;
+; @return CFLAG set if okay, clear otherwise
+; @return R16 byte received
+; @clobbers R16, R20, R21, R22 (R17)
+
+uartBitbang_ReceiveByte:
+  ldi r21, 8                                   ; bits left
+  clr r20                                      ; byte currently receiving
+  ; wait for startbit
+  rcall uartBitbang_WaitForDataLow             ; (R17, R22)
+  brcc uartBitbang_ReceiveByte_error
+  Utils_WaitNanoSecs COM_HALFBIT_LENGTH, 10, r22  ; goto middle of startbit to maximize sync stability
+uartBitbang_ReceiveByte_loop:
+    Utils_WaitNanoSecs COM_BIT_LENGTH, 8, r22  ; 8 cycles used in the complete loop between waits
+    sec                                        ; +1
+    sbic COM_RXD_DATA, COM_RXD_PIN                                ; LOW: +2, HIGH: +1
+      rjmp uartBitbang_ReceiveByte_shiftIn                           ; HIGH: +2, rjmp, use set CFLAG
+    clc                                        ; LOW: +1
+uartBitbang_ReceiveByte_shiftIn:
+    ror r20                                    ; +1
+    dec r21                                    ; +1
+  brne uartBitbang_ReceiveByte_loop                                  ; +2, sum per loop: 8 cycles
+  rcall uartBitbang_WaitForDataHigh            ; wait for start of stopbit
+  brcc uartBitbang_ReceiveByte_error
+  mov r16, r20
+  sec
+  ret
+uartBitbang_ReceiveByte_error:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_WaitForDataLow
+;
+; Wait for data pin to become low
+; @return CFLAG set if okay, clear otherwise
+; @clobbers R17, R22
+
+uartBitbang_WaitForDataLow:
+  UART_BB_M_WAIT_FOR_PIN_LOW COM_RXD_DATA, COM_RXD_PIN
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_WaitForDataHigh
+;
+; Wait for data pin to become high
+; @return CFLAG set if okay, clear otherwise
+; @clobbers R17, R22
+
+uartBitbang_WaitForDataHigh:
+  UART_BB_M_WAIT_FOR_PIN_LOW COM_RXD_DATA, COM_RXD_PIN
+  ret
+; @end
+
+
+
+
+
diff --git a/avr/modules/uart_bitbang/defs.asm b/avr/modules/uart_bitbang/defs.asm
new file mode 100644
index 0000000..9485944
--- /dev/null
+++ b/avr/modules/uart_bitbang/defs.asm
@@ -0,0 +1,13 @@
+; ***************************************************************************
+; copyright   : (C) 2024 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.   *
+; ***************************************************************************
+
+
+.equ UART_BITBANG_BUFFER_NUM  = 4
+
+
diff --git a/avr/modules/uart_bitbang/main.asm b/avr/modules/uart_bitbang/main.asm
new file mode 100644
index 0000000..ca10971
--- /dev/null
+++ b/avr/modules/uart_bitbang/main.asm
@@ -0,0 +1,398 @@
+; ***************************************************************************
+; copyright   : (C) 2024 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.   *
+; ***************************************************************************
+
+
+
+; UART_BitBang_Init
+; UART_BitBang_Fini
+; UART_BitBang_Run
+; UART_BitBang_SendPacket:
+; UART_BitBang_GetNextReceivedPacket:
+; UART_BitBang_ReleaseReceivedPacket:
+
+
+.include "modules/com2/buffer.asm"
+
+
+
+.dseg
+
+
+uartBitbangDataBegin:
+  uartBitbangRecvBuffersUsed:     .byte 1
+  uartBitbangMaxBuffersUsed:      .byte 1
+  uartBitbangRecvBuffersWritePos: .byte 1
+  uartBitbangRecvBuffersReadPos:  .byte 1
+  uartBitbangRecvBuffers:         .byte COM2_BUFFER_SIZE*UART_BITBANG_BUFFER_NUM
+uartBitbangDataEnd:
+
+
+
+
+.cseg
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_Init
+;
+; @return CFLAG set if okay, clear on error
+; @clobbers R16, R17, X, Y
+
+UART_BitBang_Init:
+  ; preset SRAM data area
+  ldi xh, HIGH(uartBitbangDataBegin)
+  ldi xl, LOW(uartBitbangDataBegin)
+  clr r16
+  ldi r17, (uartBitbangDataEnd-uartBitbangDataBegin)
+  rcall Utils_FillSram
+
+  ; setup pins and interrupts
+  cbi COM_TXD_DATA, COM_TXD_PIN           ; disable internal pullup for TXD
+  cbi COM_TXD_DDR, COM_TXD_PIN            ; set TXD port as input
+
+  cbi COM_RXD_DATA, COM_RXD_PIN           ; disable internal pullup for RXD
+  cbi COM_RXD_DDR, COM_RXD_PIN            ; set RXD port as input
+
+  cbi COM_ATTN_OUTPUT, COM_ATTN_PIN       ; disable internal pullup for ATTN
+  cbi COM_ATTN_DDR, COM_ATTN_PIN          ; set ATTN port as input
+
+  sbi COM_IRQ_ADDR_ATTN, COM_IRQ_BIT_ATTN ; enable pin change irq for ATTN line
+  in r16, GIMSK                           ; enable pin change irq PCIE0 or PCIE1
+  ori r16, (1<<COM_IRQ_GIMSK_ATTN)
+  out GIMSK, R16
+  
+  ldi r16, (1<<COM_IRQ_GIFR_ATTN)         ; clear pending irq by writing 1 to ATTN bit
+  out GIFR, r16
+  
+  sec
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_Init
+;
+; @return CFLAG set if okay, clear on error
+; @clobbers R16, R17, X, Y
+
+UART_BitBang_Fini:
+  cbi COM_TXD_DDR, COM_TXD_PIN            ; set TXD port as input
+  cbi COM_RXD_DDR, COM_RXD_PIN            ; set RXD port as input
+  cbi COM_ATTN_DDR, COM_ATTN_PIN          ; set ATTN port as input
+
+  cbi COM_IRQ_ADDR_ATTN, COM_IRQ_BIT_ATTN ; disable pin change irq for ATTN line
+  in r16, GIMSK                           ; enable pin change irq PCIE0 or PCIE1
+  andi r16, ~(1<<COM_IRQ_GIMSK_ATTN)
+  out GIMSK, R16
+  
+  ldi r16, (1<<COM_IRQ_GIFR_ATTN)         ; clear pending irq by writing 1 to ATTN bit
+  out GIFR, r16
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_Run
+;
+; @clobbers any
+
+UART_BitBang_Run:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_SendPacket
+; Send packet, if line free.
+;
+; @param X buffer to send
+; @return CFLAG: set if okay (packet sent), cleared on error
+; @clobbers r22, x (r18, r19, r22)
+
+UART_BitBang_SendPacket:
+  rcall uartBitbang_SendPacket
+  brcs UART_BitBang_SendPacket_okay
+  cpi r16, COM2_ERROR_BUSY
+  breq UART_BitBang_SendPacket_busyError
+  cpi r16, COM2_ERROR_COLLISION
+  breq UART_BitBang_SendPacket_collError
+  ; fall-through
+UART_BitBang_SendPacket_busyError:
+  ldi xl, LOW(com2StatsBusyError)
+  ldi xh, HIGH(com2StatsBusyError)
+  rjmp UART_BitBang_SendPacket_incCounterRetNc
+UART_BitBang_SendPacket_collError:
+  ldi xl, LOW(com2StatsCollisions)
+  ldi xh, HIGH(com2StatsCollisions)
+UART_BitBang_SendPacket_incCounterRetNc:
+  rcall Utils_IncrementCounter16                 ; (r18, r19, r22)
+  clc
+  ret
+UART_BitBang_SendPacket_okay:
+  ldi xl, LOW(com2StatsPacketsOut)
+  ldi xh, HIGH(com2StatsPacketsOut)
+  rcall Utils_IncrementCounter16                 ; (r18, r19, r22)
+  sec
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_GetNextReceivedPacket
+;
+; Get next received packet from receiption buffers. 
+; Call @ref UART_BitBang_ReleaseReceivedPacket to release the packet buffer.
+;
+; @return CFLAG set if okay (packet received), cleared on error
+; @return X pointer to packet received
+; @clobbers r16, r17
+
+UART_BitBang_GetNextReceivedPacket:
+  lds r16, uartBitbangRecvBuffersUsed
+  tst r16
+  breq UART_BitBang_GetNextReceivedPacket_retNc  ; no buffers in use
+  lds r16, uartBitbangRecvBuffersReadPos
+  rcall uartBitbang_BufferPosToX                 ; get current read buffer to X (R16, R17)
+  sec
+  ret
+UART_BitBang_GetNextReceivedPacket_retNc:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine UART_BitBang_ReleaseReceivedPacket
+;
+; Release first packet in queue from from receiption buffers (i.e. the one returned
+; by @ref UART_BitBang_GetNextReceivedPacket)
+;
+; @clobbers r16, r17, r21
+
+UART_BitBang_ReleaseReceivedPacket:
+  rjmp COM2_BufferDeallocFront                       ; (r16, r17, r21)
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_ReceivePacket
+;
+; Receive packet.
+;
+; @return CFLAG set if okay (packet received), cleared on error
+; @clobbers r16, r17, x (r18, r19, r20, r21, r22)
+
+uartBitbang_ReceivePacket:
+  rcall uartBitbang_BufferAlloc                 ; (r16, r17, r21)
+  brcs uartBitbang_ReceivePacket_bufferAvailable
+  
+  ldi xl, LOW(com2StatsNoBufferError)           ; buffer in use, don't release
+  ldi xh, HIGH(com2StatsNoBufferError)          ; just increment error counter
+  rcall Utils_IncrementCounter16                ; (r18, r19, 22)
+  clc
+  ret
+uartBitbang_ReceivePacket_bufferAvailable:
+  push xl
+    push xh
+      lds r16, com2Address
+      ldi r17, (COM2_BUFFER_SIZE-3)             ; buffer size minus dst addr, payload len, crc byte
+      rcall uartBitbang_ReceivePacketIntoBuffer ; r16, r17, r18, X (r19, r20, r21, r22)
+    pop xh
+  pop xl
+  brcc uartBitbang_ReceivePacket_error
+
+  rcall com2CheckMessageInBuffer                ; (R16, R17, R18, R19, R20, X)
+  brcc uartBitbang_ReceivePacket_dataError
+
+  ; everything okay
+  ldi xl, LOW(com2StatsPacketsIn)
+  ldi xh, HIGH(com2StatsPacketsIn)
+  rcall Utils_IncrementCounter16         ; (r18, r19, 22)
+  sec
+  ret
+
+uartBitbang_ReceivePacket_error:
+  cpi r16, COM2_ERROR_NOTFORME
+  breq uartBitbang_ReceivePacket_notForMe
+  cpi r16, COM2_ERROR_DATAERROR
+  breq uartBitbang_ReceivePacket_dataError
+  ;cpi r16, COM2_ERROR_IOERROR               
+  ;breq uartBitbang_ReceivePacket_ioError
+  ;rjmp uartBitbang_ReceivePacket_retnc
+  rjmp uartBitbang_ReceivePacket_ioError     ; default to IO ERROR
+uartBitbang_ReceivePacket_ioError:
+  ldi xl, LOW(com2StatsIoError)
+  ldi xh, HIGH(com2StatsIoError)
+  rjmp uartBitbang_ReceivePacket_incCounterDeallocNc
+uartBitbang_ReceivePacket_dataError:
+  ldi xl, LOW(com2StatsContentError)
+  ldi xh, HIGH(com2StatsContentError)
+  rjmp uartBitbang_ReceivePacket_incCounterDeallocNc
+uartBitbang_ReceivePacket_notForMe:
+  ldi xl, LOW(com2StatsNotForMe)
+  ldi xh, HIGH(com2StatsNotForMe)
+  rjmp uartBitbang_ReceivePacket_incCounterDeallocNc
+uartBitbang_ReceivePacket_incCounterDeallocNc:
+  rcall Utils_IncrementCounter16         ; (r18, r19, 22)
+uartBitbang_ReceivePacket_deallocRetnc:
+  rcall uartBitbang_BufferDeallocBack
+uartBitbang_ReceivePacket_retnc:
+  clc
+  ret
+; @end
+
+
+
+
+
+
+
+
+
+; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+; Buffer Management
+; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_BufferAlloc
+;
+; Allocate a transfer buffer.
+;
+; @return CFLAG set if okay, clear otherwise
+; @return X     pointer to allocated buffer in SRAM
+; @clobbers r16, r17, r21
+
+uartBitbang_BufferAlloc:
+  COM2_M_BufferAlloc UART_BITBANG_BUFFER_NUM, uartBitbangMaxBuffersUsed, uartBitbangRecvBuffersUsed, uartBitbangRecvBuffersWritePos
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_BufferDeallocBack
+;
+; Release a transfer buffer at the end of the list by decreasing the write pos.
+; This releases the last allocated buffer!
+;
+; @return CFLAG set if okay, clear otherwise
+; @clobbers r16, r17, r21
+
+uartBitbang_BufferDeallocBack:
+  COM2_M_BufferDeallocBack UART_BITBANG_BUFFER_NUM, uartBitbangRecvBuffersUsed, uartBitbangRecvBuffersWritePos
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_BufferDeallocFront
+;
+; Release a transfer buffer by increasing the read pos.
+;
+; @return CFLAG set if okay, clear otherwise
+; @clobbers r16, r17, r21
+
+uartBitbang_BufferDeallocFront:
+  COM2_M_BufferDeallocFront UART_BITBANG_BUFFER_NUM, uartBitbangRecvBuffersUsed, uartBitbangRecvBuffersReadPos
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_BufferPosToX
+;
+; Get a pointer to the SRAM position of the given buffer.
+; CAVE: Code must correspond to COM2_BUFFER_SIZE!!
+;
+; @param  R16 buffer number (starting with 0)
+; @return X   pointer to buffer in SRAM
+; @clobbers R16, R17
+
+uartBitbang_BufferPosToX:
+  COM2_M_BufferPosToX uartBitbangRecvBuffers
+  ret
+; @end
+
+
+
+
+
+
+
+
+
+
+; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+; ISR
+; +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+
+uartBitbangIsrPcint0:
+  push r15
+    in r15, SREG
+    sbic COM_ATTN_INPUT, COM_ATTN_PIN
+      rjmp uartBitbangIsrPcint0_end
+    ; low, read packet
+    push r1
+      push r16
+        push r17
+          push r18
+            push r19
+              push r20
+                push r21
+                  push r22
+                    push xh
+                     push xl
+                       push r15
+                         rcall uartBitbang_ReceivePacket ; (r16, r17, r18, r19, r20, r21, r22, x)
+                       pop r15
+                       lds xl, com2Interrupts
+                       lds xh, com2Interrupts+1
+                       adiw xh:xl, 1
+                       sts com2Interrupts, xl
+                       sts com2Interrupts+1, xh
+                     pop xl
+                    pop xh
+                  pop r22
+                pop r21
+              pop r20
+            pop r19
+          pop r18
+        pop r17
+      pop r16
+    pop r1
+uartBitbangIsrPcint0_end:
+    out SREG, r15
+  pop r15
+  reti
+
+
+
+; set routine functions
+.equ COMIO_Init = UART_BitBang_Init
+.equ COMIO_Fini = UART_BitBang_Fini
+.equ COMIO_Run = UART_BitBang_Run
+.equ COMIO_SendPacket = UART_BitBang_SendPacket
+.equ COMIO_GetNextReceivedPacket = UART_BitBang_GetNextReceivedPacket
+.equ COMIO_ReleaseReceivedPacket = UART_BitBang_ReleaseReceivedPacket
+
+
diff --git a/avr/modules/uart_bitbang/packetlevel.asm b/avr/modules/uart_bitbang/packetlevel.asm
new file mode 100644
index 0000000..5c8e4b2
--- /dev/null
+++ b/avr/modules/uart_bitbang/packetlevel.asm
@@ -0,0 +1,159 @@
+; ***************************************************************************
+; copyright   : (C) 2024 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.   *
+; ***************************************************************************
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_ReceivePacketIntoBuffer
+;
+; Receive a packet into buffer pointed to by X.
+; Expects interrupts to be disabled.
+;
+; @param R16 COM address to listen to
+; @param R17 maximum value for accepted msg data (i.e. buffersize minus 3)
+; @param X   buffer to receive to
+; @return CFLAG set if okay (packet received), cleared on error
+; @return R16 error code if CFLAG is cleared (COM2_ERROR_NOTFORME, COM2_ERROR_IOERROR, COM2_ERROR_DATAERROR)
+; @clobbers: r16, r17, r18, X (r19, r20, r21, r22)
+
+uartBitbang_ReceivePacketIntoBuffer:
+  mov r18, r17
+  push r16
+    ; read destination address
+    rcall uartBitbang_ReceiveByte             ; read byte (R16, R17, R20, R21, R22)
+  pop r17                                     ; pop from R16 to R17
+  brcc uartBitbang_ReceivePacketIntoBuffer_ioError
+#ifdef COM_ACCEPT_ALL_DEST                    ; accept every destination address
+  rjmp uartBitbang_ReceivePacketIntoBuffer_acceptAddr
+#else
+  ; compare destination address (accept "FF" and own address)
+  cp r16, r17
+  breq uartBitbang_ReceivePacketIntoBuffer_acceptAddr
+  cpi r16, 0xff
+  breq uartBitbang_ReceivePacketIntoBuffer_acceptAddr
+  ldi r16, COM2_ERROR_NOTFORME
+  rjmp uartBitbang_ReceivePacketIntoBuffer_error        ; clc/ret
+#endif
+uartBitbang_ReceivePacketIntoBuffer_acceptAddr:
+  st X+, r16                                  ; store dest address, lock buffer
+  ; read msg length
+  rcall uartBitbang_ReceiveByte               ; read packet length (R16, R17, R20, R21, R22)
+  brcc uartBitbang_ReceivePacketIntoBuffer_ioError
+  st X+, r16
+  cp r16, r18                                 ; (COM2_BUFFER_SIZE-3)
+  brcc uartBitbang_ReceivePacketIntoBuffer_contentError ; packet too long
+  inc r16                                     ; account for checksum byte
+  mov r17, r16
+uartBitbang_ReceivePacketIntoBuffer_loop:
+    push r17
+      rcall uartBitbang_ReceiveByte           ; read byte (R16, R17, R20, R21, R22)
+    pop r17
+    brcc uartBitbang_ReceivePacketIntoBuffer_ioError
+    st X+, r16
+    dec r17
+  brne uartBitbang_ReceivePacketIntoBuffer_loop
+  sec
+  ret
+uartBitbang_ReceivePacketIntoBuffer_ioError:
+  ldi r16, COM2_ERROR_IOERROR
+  rjmp uartBitbang_ReceivePacketIntoBuffer_error
+uartBitbang_ReceivePacketIntoBuffer_contentError:
+  ldi r16, COM2_ERROR_DATAERROR
+uartBitbang_ReceivePacketIntoBuffer_error:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_SendPacket
+;
+; Send packet over wire, handle ATTN line.
+;
+; @param  X ptr to buffer to send
+; @return CFLAGS set if okay, cleared otherwise (errorcode in R16)
+; @clobbers R16, R22 (R17, R21, X)
+
+uartBitbang_SendPacket:
+  rcall uartBitbang_AcquireBus
+  brcc uartBitbang_SendPacket_lineBusyError
+  
+  rcall uartBitbang_WaitForOneBitLength          ; wait for one bit duration (R22)
+  rcall uartBitbang_WaitForOneBitLength          ; wait for one bit duration (R22)
+
+  adiw xh:xl, COM2_MSG_OFFS_MSGLEN
+  ld r17, X
+  sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
+  inc r17                                        ; account for dest addr
+  inc r17                                        ; account for msglen byte
+  inc r17                                        ; account for crc byte
+
+uartBitbang_SendPacket_loop:
+    ld r16, X+
+    rcall uartBitbang_SendByte                   ; send byte (R16, R21, R22)
+    brcc uartBitbang_SendPacket_releaseBusRet
+    dec r17
+  brne uartBitbang_SendPacket_loop
+  sec
+uartBitbang_SendPacket_releaseBusRet:
+  cbi COM_ATTN_DDR, COM_ATTN_PIN                 ; release ATTN line (by setting direction to IN)
+  brcc uartBitbang_SendPacket_ioError
+  ; packet successfully sent
+  ret
+uartBitbang_SendPacket_ioError:
+  ldi r16,COM2_ERROR_COLLISION
+  ret
+uartBitbang_SendPacket_lineBusyError:
+  ldi r16,COM2_ERROR_BUSY
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_AcquireBus
+;
+; Reserve bus if free (otherwise return error)
+; Expects interrupts to be disabled.
+;
+; @return CFLAG set if okay (bus acquired), cleared on error
+; @clobbers: none
+
+uartBitbang_AcquireBus:
+  ; check for ATTN line: busy?
+  cbi COM_ATTN_OUTPUT, COM_ATTN_PIN              ; disable pullup on ATTN
+  cbi COM_ATTN_DDR, COM_ATTN_PIN                 ; set ATTN as input
+  nop                                            ; needed to sample current input
+  sbis COM_ATTN_INPUT, COM_ATTN_PIN              ; ATTN low?
+    rjmp uartBitbang_AcquireBus_busy             ; jump if it is
+  cbi COM_ATTN_OUTPUT, COM_ATTN_PIN              ; set ATTN low
+  sbi COM_ATTN_DDR, COM_ATTN_PIN                 ; set ATTN as output
+  sec
+  ret
+uartBitbang_AcquireBus_busy:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartBitbang_WaitForOneBitLength
+;
+; wait for one bit length (minus cycles for call and ret).
+;
+; @clobbers r22
+
+uartBitbang_WaitForOneBitLength:
+  Utils_WaitNanoSecs COM_BIT_LENGTH, 7, r22       ; wait for one bit duration (minus RCALL/RET)
+  ret
+; @end
+
+