Hi, I am working on a home brew SBC and am trying to build a serial cable for it. Are there any RS-232 serial port gurus who could help me plumb out a custom cable? The SBC serial connection works but as it currently is configured it only works as 3 wire serial with no flow control (ie, RD, TD, & GND pins). I would very much like to make the serial cable and SBC support hardware flow control. Having the DSR/DTR pins connected should allow it. However the PC is expecting CTS/RTS hardware flow control. My SBC UART is wired so that the RD, TD, DTR, DSR, and GND pins are brought to the serial connector. I probably should have brought CTS & RTS out but it is too late to change it now. I have wired a cable like this which works for 3 wire serial (no flow control) PC DB25 (9 to 25 pin cable) SBC (25 pin female) 2 TD----------------------RD 3 RD----------------------TD 7 GND---------------------GND 6 DSR---------------------DTR 20 DTR---------------------DSR Obviously this cable does not support hardware flow control because when I try to connect with hardware flow control enabled, I can see the SBC boot message on the terminal screen but cannot send characters from the PC to the SBC. So I have been experimenting trying to figure out how to fix this. I got the data sheet for the 16C550 and a serial port breakout box. After much combinations, I discovered that if I connect a jumper between the PC serial port pins 5 (PC CTS) and pin 20 (SBC DSR) then the serial port *DOES* support hardware flow control. At least it appears to. I get the feeling though that I am mixing dissimilar control signals and it is confusing me. My question is, does the above configuration with the PC CTS and SBC DSR connected really use hardware flow control or is it just "faking out" the PC and/or SBC UART? As a follow on, are both sides actually getting hardware flow control or is it just one side or the other? This is my new and improved serial cable with *appears* to support hardware flow control. Is there any way to test this? PC DB25 (9 to 25 pin cable) SBC (25 pin female) 2 TD----------------------RD 3 RD----------------------TD 7 GND---------------------GND 6 DSR---------------------DTR 20 DTR----+----------------DSR 5 CTS----+ Thanks in advance for any help! Andrew Lynch