Add comment to explain the complex naming scheme of COMs on Win32

Reported by Marco Sala.

Add comment to explain the complex naming scheme of COMs on Win32
Reported by Marco Sala.
Stéphane Raimbault
1 parent b1423d73
Showing 1 changed file with 4 additions and 1 deletions
src/modbus-rtu.c
@@ -805,7 +805,10 @@ const modbus_backend_t _modbus_rtu_backend = {
  
 /* Allocate and initialize the modbus_t structure for RTU
    - device: "/dev/ttyS0"
-   - baud:   9600, 19200, 57600, 115200, etc
+     On Win32, it's necessary to prepend COM name with "\\.\" for COM number
+     greater than 9, eg. "\\\\.\\COM10". See
+     http://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx for details.
+   - baud: 9600, 19200, 57600, 115200, etc
    - parity: 'N' stands for None, 'E' for Even and 'O' for odd
    - data_bits: 5, 6, 7, 8
    - stop_bits: 1, 2