TCP/IP TO HDLC (RS485) SERIAL GATEWAY

[ian bell_1]

I need to read and write a TCP/IP stream from an Itanium via ethernet (using OpenVMS) to a RS485, 180Kbaud, HDLC format.

Any help would be greatly appreciated.

[Art Wiens]

Well one would have to assume that the remote serial device is also connected to ethernet somehow (or else this project is a non-starter ;-).

That serial to ethernet "adapter" device should have an associated ip address and offer some available ports/protocols for access.

The manufacturer of this device might even have some sample code for developers to look at.

Other than that, your question is a bit terse as to what kind of help you need.

Cheers,
Art

[Brian Reiter]

I was going to suggest something like the Control DeviceMaster - but a 180K baud? Outside its range I think.

[Robert Gezelter]

Ian,

Having done similar applications in the past, there are many issues that will arise. HDLC is (as I recall from memory, I am not in my library at the moment), a synchronous protocol. Put plainly, that means that for all intents and purposes, entire blocks must be sent precisely, one character after another with no gaps.

This generally means that entire HDLC blocks need to be sent as single messages over the network. A network delay in the middle of a message would force retransmission. CSMA/CD networks like Ethernet/IEEE 802.3 are subject to random latency delays caused by collision backoffs. It seems counter-intuitive, but even a 1Gb Ethernet is subject to these latencies at times. On a 180Kb synchonous serial circuit, that means that each character must be available at 1/180000 intervals.

More information would certainly be useful.

If this needs to be taken offline, I will be happy to speak with you.

- Bob Gezelter, http://www.rlgsc.com