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From: jrv@siemens.UUCP
Newsgroups: net.micro.pc
Subject: Re: 9 pin serial port on PC AT
Message-ID: <23900008@siemens.UUCP>
Date: Thu, 27-Feb-86 11:07:00 EST
Article-I.D.: siemens.23900008
Posted: Thu Feb 27 11:07:00 1986
Date-Received: Sat, 1-Mar-86 03:13:04 EST
References: <734@harvard.UUCP>
Lines: 45
Nf-ID: #R:harvard:-73400:siemens:23900008:000:1565
Nf-From: siemens!jrv    Feb 27 11:07:00 1986


>/* Written  2:22 pm  Feb 25, 1986 by mason@noscvax in siemens:net.micro.pc */
>In article <734@harvard.UUCP> kevin@harvard.UUCP (Kevin Crowston) writes:
>>Can anyone post or repost a mapping from the AT's 9 pins
>>to (say) the 25 pins of an RS-232 DTE connector?
>
>PC 9 pin to 25 pin connection
>
>    1 ---- 8
>    2 ---- 3
>    3 ---- 2
>    4 ---- 20
>    5 ---- 7
>    6 ---- 6
>    7 ---- 4
>    8 ---- 5
>    9 ---- 22

I do not agree with this mapping. It looks like a mapping to a DCE 25 pin
connection and not DTE as was requested.

PC 9 pin			25 pin DTE connection

1 (Carrier Detect) <------------ no connection
2 (Data Input) <---------------- 2 - TxD (Transmit data)
3 (Data Output) ---------------> 3 - RxD (Received data)
4 (DTR) ------------------+----> 6 - DSR
                          +----> 8 - CD (carrier detect)
5 (Signal Ground) -------------- 7 - SGND (Signal Ground)
6 (DSR) <----------------------- 20 - DTR
7 (RTS) ----->+-loop  loop-+<--- 4 - RTS
8 (CTS) <-----+            +---> 5 - CTS
9 (Ring indicator) <------------ no connection

If you are going to be running interrupts on the serial port then you
might want to tie pins 1 and 9 to pin 4 to prevent any spurious
interrupts from ocurring. This is the connection I used recently
to connect a VT220 to the AT serial port. (Actually, I tied pins
1, 6, 9 to pin 4 and made DTR active. On the 25 pin DTE side I connected
pin 6(DSR) and 8(CD) to pin 20(DTR) to get things going.)

If you have any problems get in touch with e-mail.

Jim Vallino
{allegra,ihnp4}!princeton!siemens!jrv