bwrdmond@vax1.tcd.ie (05/26/91)
Is there such a beast as a "Null Terminal" cable - i.e. a DCE to DCE
connection?
If a modem will respond to RTS by raising CTS even while DTR is low then it
seems fairly straightforward. Is this the case?
Regards,
Brian peter@ficc.ferranti.com (Peter da Silva) (05/27/91)
A "full" null modem cable works DCE-DCE or DTE-DTE, and usually looks something like: 1-1 2-3 3-2 4-5 5-4 6-8+20 7-7 8+20-6. -- Peter da Silva; Ferranti International Controls Corporation; +1 713 274 5180; Sugar Land, TX 77487-5012; `-_-' "Have you hugged your wolf, today?"
root@zswamp.uucp (Geoffrey Welsh) (05/28/91)
>From: bwrdmond@vax1.tcd.ie >Is there such a beast as a "Null Terminal" cable - i.e. a >DCE to DCE connection? Offhand, I'd say that you *might* be able to use a null modem cable to accomplish this, even though an ideal null terminal cable ("DCE bridge"?) might need to be wired differently. >If a modem will respond to RTS by raising CTS even while DTR >is low then it seems fairly straightforward. Is this the case? Not with dialup async modems, which either leave CTS asserted and ignore RTS (dy default, anyway) or use them for hardware flow control. In that case, one modem's CTS output would have to be wired to the other's RTS input; DSR (effectively 'modem ready') should be wired to the other modem's DTR (effectively 'modem enable') and (of course), the TxD and RxD should be crossed. Sounds a bit like the null modem cables I use. I suppose that you should wire the thing such that DTR drops for about two seconds when carrier detect goes from true to false, but that makes this a device as much as a cable. These specs are by no means complete. -- Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171) root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root 602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553 "He who claims to know everything can't possibly know much" -me
root@zswamp.uucp (Geoffrey Welsh) (05/28/91)
In a letter to All, Peter da Silva (peter@ficc.ferranti.com ) wrote: >A "full" null modem cable works DCE-DCE or DTE-DTE, and >usually looks something like: > 1-1 2-3 3-2 4-5 5-4 6-8+20 7-7 8+20-6. That's one approach to a null modem (feeding DTR back to DCD locally); I prefer to feed it to the *opposite* DCD, so each device senses carrier whenever the other is ready. However, for a DCE, pins 8 and 20 are both outputs; tying them together is definitely *not* robust under your pinouts or mine. -- Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171) root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root 602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553 "He who claims to know everything can't possibly know much" -me