Path: utzoo!utgpu!water!watmath!clyde!att!ucbvax!UMAXC.WEEG.UIOWA.EDU!jnford
From: jnford@UMAXC.WEEG.UIOWA.EDU (Jay Ford)
Newsgroups: comp.sys.encore
Subject: Annex hardware flow control
Message-ID: <8808171830.AA05607@umaxc.weeg.uiowa.edu>
Date: 17 Aug 88 18:30:17 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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At The University of Iowa, we have a need to use hardware flow control and
carrier detection independently on our Annex ports.  This is not an
unreasonable expectation, and apparently not an uncommon one since this
problem was discussed in a recent note sent to the info-encore mailing list.
However, the Annex only allows the use of one of these schemes at a time:
either carrier detection OR hardware flow control; not both.

According to the "Annex Hardware Installation Guide", the pin/signal
allocations are as follows:
	pin	lead name		lead description
	---	---------		----------------
	  1	chasis ground		chasis ground
	  2	TxD			transmit data
	  3	RxD			receive data
	  4	NC			not used  (usually RTS)
	  5	CTS			clear to send (low true)
	  6	NC			not used
	  7	signal ground		signal ground
	  8	NC			not used  (usually CD)
	  9	DTR			data terminal ready
There is neither an RTS lead required for hardware flow control
nor a CD lead needed for true carrier detection.

Also, the cables offered by Encore allow the following connections:
	Annex port	25-pin port	use for cable
	----------	-----------	-------------
	CTS		DTR		null modem
	DTR		CTS		null modem

	CTS		CD		Hayes-style asynchronous modem
	DTR		DTR		Hayes-style asynchronous modem
Neither of these cabling arrangements provides both hardware flow control
and carrier detection.

A solution to this problem is the use of the currently unused pins for
RTS (pin 4) and CD (pin 8).  This would allow for real carrier
detection and RTS-CTS hardware flow control simultaneously.
Of course, this would require corresponding software changes.


Jay Ford
Weeg Computing Center
University of Iowa
jnford@umaxc.weeg.uiowa.edu
(319) 335-5555