Date: Wed, 16 Jan 2002 13:04:38 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Bernd Walter <ticso@cicely8.cicely.de> Cc: Trevor Johnson <trevor@jpj.net>, Riccardo.Veraldi@fi.infn.it, freebsd-alpha@FreeBSD.ORG Subject: Re: DEC3000/300 Message-ID: <3C45EAE6.CF12B5C5@mindspring.com> References: <20020116023458.E17814-100000@blues.jpj.net> <3C45DF84.5990A4E4@mindspring.com> <20020116214931.M50371@cicely8.cicely.de>
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Bernd Walter wrote: > > A real NULL-modem cable looks like: > > > > TX -------- RX > > RX -------- TX > > CTS -------- RTS > > RTS -------- CTS > > GND -------- GND (signal ground, not chassis ground) > > DCD -------- DTR > > DTR -------- DCD > > GND -------- (chassis ground on one end to all other wires) > > I usually additionaly bridge DSR with DCD on both sides just in > case I need to use it for designs requiring DSR. I considered that, but these are DTE interfaces, not DCE, so it makes no sense. If I knew it was DTE<->DCE or DCE<->DTE, I would have tied DSR on one side to DSR and DTR on the other for both sides, per Technical Aspects of Data Communications John McNamara Digital Press ASIN: 1555581110 (I don't know why I always think this was by McKneely; in any case, for $5 used on Amazon, this is a cheap way to get some neat information, including the Bell 103 and 202 standards, which are expensive to get elsewhere). As it is, you could end up with +11v <-> +11v, and with the signal grounds tied and the chassis ground untied, you could get a ground loop (best case) or cook a TTL chip (worst case, assuming a multiport chip or multiple connections per pinout internally). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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