From 7c4cb13bbcfc7869e0ac7f5c623ecf2f7eea76d7 Mon Sep 17 00:00:00 2001
From: Stéphane Raimbault <stephane.raimbault@gmail.com>
Date: Mon, 10 Jan 2011 19:30:47 +0100
Subject: [PATCH] Add comment to explain the complex naming scheme of COMs on Win32

---
 src/modbus-rtu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index f80de59..e813842 100644
--- a/src/modbus-rtu.c
+++ b/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
--
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