diff --git a/avr/modules/com2w/com2w.asm b/avr/modules/com2w/com2w.asm
index 31bd832c..9f1af11b 100644
--- a/avr/modules/com2w/com2w.asm
+++ b/avr/modules/com2w/com2w.asm
@@ -844,5 +844,31 @@ com2wPcintIsr_end:
 
 
 
+; ---------------------------------------------------------------------------
+; @routine COM2W_CheckPort @global
+;
+; @param r16 port value at IRQ time (e.g. PINA)
+; @param Y pointer to interface
+; @clobbers: r16, r17, r18, r19, r20, r21, r22, r24, r25, X, Y
+
+COM2W_CheckPort:
+  ldi yl, LOW(com2w_iface)
+  ldi yh, HIGH(com2w_iface)
+  ldd r17, Y+NET_IFACE_OFFS_LASTPORTVALUE
+  std Y+NET_IFACE_OFFS_LASTPORTVALUE, r16
+  mov r18, r17
+  eor r18, r16                  ; changed bits=1
+  com r18                       ; complement: changed bits=0
+  or r18, r16                   ; only bits are 0 which have just changed to 0
+  sbrs r18, COM_CLK_PIN
+    rjmp COM2W_CheckPort_end
+  ; CLK just changed to 0, read packet
+  rcall com2wReceiveNextPkg     ; (R16, R17, R18, R19, R20, R21, R22, R24, R25, X)
+COM2W_CheckPort_end:
+  ret
+; @end
+
+
+
 #endif ; AVR_MODULES_COM2W_COM2W_H