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01-04-2008, 08:11 PM
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 rs422 on 8-port asynchronous adapter Hello, Using 8-port EIA 232/EIA 422 asynchronous PCI adapter on IBM RS/6000, AIX 5.1. My problem is as follows: Having a rs422 device only using Tx and Rx lines. pinout on adapter: Shell - Shield ground 2 - TxA 3 - RxA 4 - TxB 5 - RxB 7 - Signal ground Creating a tty with mkdev, specifiying rs422, adapter/port, baud rates etc. But, I am unable to write to this tty, getting an I/O error (errno 5). Found (after some searching) that: "In AIX, all tty and lp devices are modem devices. They require DCD in order to function. Ideally, DCD is wired from the device to the port." I do not have any DCD for my rs422 connection. So, I thought that i could set "Force carrier" to enable on the tty. Now I am able to write to the tty, but I do not get the expected result. After snooping on the wires, I found that forcing carrier results in always high signal on pin 4. But, of course, this pin should be used for TxB when communicating with the device. So, my questions are: - Am I completely lost, doing some stupid mistake?  - Can I use the 'altpin' option, and how would the pinout be if this is the case? Note: Communication is Ok when using rs232 tty and a rs232-rs422 converter. Also Ok using rs422 on linux system. Thanks in advance. Best regards, Anders      |
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