[Coco] Re: Supercomm: more details
John E. Malmberg
wb8tyw at qsl.net
Sun Aug 15 23:39:48 EDT 2004
KnudsenMJ at aol.com wrote:
> In a message dated 8/12/04 8:17:29 PM Eastern Daylight Time, james at skwirl.ca
>>Scratch my earlier email, DCD (Coco end) is wired to CTS and RTS (other
>> end) on my cable. Is that right? I think CTS (other) should be tied to
>> RTS (coco)..
If you are talking about the bit-banger port, the line labeled DCD is
treated sometimes like a CTS line by the software, and sometimes like a
Otherwise, CTS to RTS, DTR to DSR, and DCD connected to DTR on the same
side for NULL modem.
> Nope -- it's already correct. RTS should be wired to the same end's CTS (so
> each end always gives itself permission to send),
> and to the other end's DCD so the other end knows there's data about to come in.
No, that is a bug, and violates CCIT requirements. DCD on a null modem
is connected to DTR on the same connector.
DCD is a link level signal, not a flow control signal. If not present,
it follows DSR/DTR not CTS.
Some serial interfaces on some host computers implement the handling of
these signals in hardware or in the serial device drivers, and can not
support such a miswired cable that ties DCD to a CTS signal if the CTS
signal is actually being used for handshaking.
A host computer is supposed to treat a loss of DCD or DSR as the
termination of the serial session.
So is a DCE device such as a modem or a communication multiplexer.
Please do not advocate using a wiring configuration that violates CCIT
signaling requirements unless it is required to get around a hardware or
software bug that can not be fixed otherwise.
Personal Opinion Only
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