help needed for RS422 Serial Comm

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Aug 1, 2007, 10:21:49 AM8/1/07
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 why it
didnt work out is that by
the time the receiver wants to read in the data, no more data exist on
the line
for it to be read in..

Thks alot for whatever advice u may provide.


Aug 2, 2007, 3:16:48 AM8/2/07
I tested my codes using the RS232 interface, i.e COM1 and COM2 on my
PC, it works perfectly fine, can send n recv data. However, when i use
the codes on my RS422 PCI card which has 2 COM ports, com 3 and 4, it
cannot perform send and receive.

anyone knows if the cables needed for RS232 and RS422 transmission are


Aug 2, 2007, 4:39:22 AM8/2/07

The pin out for RS232 and RS422 are different, hence the cable i used
for RS232 cannot be used on the 2 COM ports on this RS422 PCI card.

I understand that I can self produce the cable based on the pin
layout, but Does anyone know if there exists a RS422 cable in the

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