Ruud writes to Andre: > I want to react on your "Network page": > > > The asynchrounous communication will be derived from the RS232 > > specification, in that normal UART 16550 or ACIA 6551 chips can be used. > > Very nice. (I always used the 8250 and 16450 with 65xx-systems) Are there any odd interfacing issues? (R/W vs /IOR and /IOW kinds of stuff) > > The physical layer could be derived from the RS485 specifications. > > The original RS485 specification uses a terminated bus, and allows > > one master to send at any time only. Otherwise drivers could be damaged. > > Can you give me in a few lines some more specifications, please? How many > lines does it use? Why can the drivers be damaged? What ICs does it use? Years ago, I put together a proposed network interface for the Amiga with a guy at Zenith, Jeff Easton. We never finished the projects, but the schematics (in HPGL and PCL) are still kicking around on Aminet (ftp://wuarchive.wustl.edu/pub/aminet/hard/hack/pocket.lzh). Someone at Commodore (Dave Haynie, IIRC), kept putting a similar circuit on new Amiga designs, and management kept takingit out, but it was RS-485 based (thus the point of mentioning it). We used the COM20010 (or COM20020) integrated ARCnet chip and an SN75176 RS-485 driver. Yes, the network was terminated, but I don't remember if there was a prohibition about multiple simultaneous transmitters; it's been too long. I'd have to check the 75176 data sheets (it's made by National Semiconductor and TI, if anybody want to dig for themselves). The COM20010 implemented a token passing bus, if using twisted-pair drivers. SMC had plenty of application notes, etc, in 1992; perhaps they still do if the chip is still in production. I'd recommend those docs for anyone planning on implementing a -485 token based network. The only reason why I wouldn't recommend the COM20010 chip today is availability. 16550 chips are going to be around for a long, long time, plus, you can code around them at the physical layer, should something better come along. The COM20010 only had one descendent that I knew of, the COM20020, and the only difference appeared to be how much onboard SRAM there was for buffers. On the other hand, you could implement a full ARCnet adapter with it, and 6 years ago, there were ARCnet networks to hook into. For a physical connection, Commodore was going to use a switched RCA jack like the kind at the front of most modern VCRs for external inputs. When empty, the switch would close, allowing the network to self-terminate. RJ-11's or RJ-45's are fine, too, but you've got to remember to stick in a terminator, like with Farallon's PhoneNet stuff. I suppose you could even use yellow/black on phone wire, as long as you didn't also have a PhoneNet network on the same cable. Cheers, -ethan
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