Part of a discussion on a rocket list re latency and throughput of RS232/RS422 / Ethernet and centralised vs distributed control in a rocket. There are a few gems in here that people may find worthwhile - I'll leave you to find them or decide if they exist. ________________ From: "Paul Breed" To: >Um.... hate to break it to you, but Ethernet *is* a fast serial link. I write low level ether net stuff for a living. Yes I know it is a fast serial link, alas it has things like a defined preamble, and checksum, minimum frame size etc... that is enforced in hardware. Also you can get a 1Gbps ethernet on a PC, you can't get it on a simple micro to drive your valve. Most of the single chip ethener/microcontroller solutions are 10 base T. The one fully integrated exception I know of is the freescale MCF52235 series. I know of nothing lighter weight than a Power PC with 1Gbps ethernet in hardware. So if you are talking about simple devices strung together with ethernet you are still talking about 10base T or at least 10 base T levels of performance. It also takes a lot more hardware to offer an ethernet interface than a fast RS-485. Just look at any ethener PHY compared to a MX485. 8 pins vs 32 pins for the pin reduced ethernet PHY whoose name I can't tell you because it's still under NDA. >Confusing bandwidth with latency is nearly always a bad mistake. But >I >don't agree with your analysis that (1G or 100M) ethernet is worse >that RS-232(!), provided you choose the components sensibly. In the real world as deployed by my customers 10/100 ethernet is 2:1 slower in latency. You may think this is due to a an inefficient implementation, but I have personally bench marked our ethernet stuff against all of our competitors and we are at least 2x better than any of the small ethernet interfaced modules and we are 10 to 20x better then the worst. Ethernet designs where I have personally designed both the ethernet hardware and written the low level drivers will ship more than 250K units this year. Paul _______________________________________________ aRocket@exrocketry.net http://exrocketry.net/mailman/listinfo/arocket -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist