Re: RS422 Serial Communication Codes in C++

"Jim Langston" <>
Fri, 3 Aug 2007 19:20:52 -0700
"fulltime" <> wrote in message

Hi all,

I installed a PCI bus interface board with 2 RS422 com ports on it. I
am attempting to transfer data between these 2 com ports. (for eg. com
3 send data to com 4)

The pseudo code of my main program is as follows:

1. Configure the 2 ports
2. Open both ports
3. Call sendByte () for com 3 to send data out.
4. Call readByte () for com 4 to read in data.
5. Close both ports

However, the whole program hangs inside the readByte () which is
listed below.

// Function name : CSerialComm::ReadByte
// Description : Reads a byte from the selected port
// Return type : BOOL
// Argument : BYTE& by
BOOL CSerialComm::ReadByte(BYTE& by)
BYTE byResByte;

DWORD dwBytesTxD=0;

if (ReadFile (m_hComm, &byResByte, 1, &dwBytesTxD, 0))
if (dwBytesTxD == 1)
return TRUE;
return FALSE;


Can anyone provide me with some advice?

Since the data is first sent out via com3, My intial guess is that by
the time the receiver wants to read in the data, no more data exist
for it to be read in..

This is mostly OT as it is OS specific, but OT in the case of why it is
hanging. Apparently ReadFile is "blocking". Blocking means it won't return
until data is ready to be read. The solution, however, is OT because you
need to find out in your OS how to determine if data is ready to be read.

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