diff --git a/avr/modules/uart_hw2/sync_recv.asm b/avr/modules/uart_hw2/sync_recv.asm
new file mode 100644
index 0000000..bfd8ecd
--- /dev/null
+++ b/avr/modules/uart_hw2/sync_recv.asm
@@ -0,0 +1,58 @@
+; ***************************************************************************
+; 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_UART_HW2_SYNC_H
+#define AVR_MODULES_UART_HW2_SYNC_H
+
+
+.dseg
+
+
+.cseg
+
+
+
+
+; sync length is 1000 us, so this should return:
+; -  125 for 1 MHz
+; - 1000 for 8 MHz
+
+syncRecv:
+syncRecv_waitForHigh:
+    sbis COM_DATA0_INPUT, COM_DATA0_PIN
+  rjmp syncRecv_waitForHigh
+
+  clr r24
+  clr r25
+
+syncRecv_waitForLow:
+    sbic COM_DATA0_INPUT, COM_DATA0_PIN
+  rjmp syncRecv_waitForLow
+
+syncRecv_countLow:                            ; total: +8 per loop
+    sbic COM_DATA0_INPUT, COM_DATA0_PIN       ; +1 if noskip, +2 if skip
+      rjmp syncRecv_countDone                 ; +2, total: +2 every loop, +3 in last loop
+    adiw r25:r24, 1                           ; +1
+    breq syncRecv_countError                  ; +1 if not 0, +2 if 0
+    nop                                       ; +1
+    nop                                       ; +1
+  rjmp syncRecv_countLow                      ; +2
+
+syncRecv_countError:
+  clr r24
+  clr r25
+syncRecv_countDone:
+  ret
+; @end
+
+
+
+
+#endif
+