What can anyone tell me about SerDes?

W

Thread Starter

Wes Crucius

The subject says it all... Anything that you can tell me would be appreciated. My application is inherently one master device sending a single (read: broadcast) message to as many as 64 slave devices. This message needs to go out about once every 50-80 microseconds, with very little jitter. The latency must also be VERY small, on the order of 5-10 microseconds. Then during the idle time, the remaining 40-75 microseconds, the master polls some status from each of the slaves on a round robbin basis. Polling one slave per 80 microseconds, for a total of 5.12 milliseconds for a full round-robbin cycle, would be fine. The data packets in each direction would easily fit within the 46 data-byte minimum of an ethernet frame, so I'm considering Ethernet, but am nervous of things like switch latency, especially because a multi-level star heirarchy would probably be required (or do they make 65+ port cut-through ethernet switches for less than an outrageous fortune?). It sounds like there may be some SerDes implementations that look like Dual-Ported-Ram, which from the processor overhead perspective would be great... Oh yeah, cabling lengths (200-300 FT), electrically noisy environment, and isolation requirements will probably mandate fiber instead of UTP. Could a star network be created reasonably with SerDes?

Thanks again for any feedback...
 
W
Is my question just dense, or hasn't anybody ever heard of SerDes? I thought it was the newest thing in high speed peer-peer serial comms (1.25 Gb)... What about the Ethernet approach, surely someone is doing this? I just read an article that indicated that Beckhoff has a scheme for tunneling raw Ethernet frames under the Win2k TCP/IP stack to get 7 microsecond updates for 368 bits of digital I/O, which appears to not so coincidentally be the minimum Ethernet data packet size of 46 bytes.

Surely someone on the list here must be toying with the approach?

Wes
 
C

Curt Wuollet

Most of the automation world is still toying with RS232. Can you implement this SerDes in RLL? :^)

Regards

cww
 
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