Path: utzoo!attcan!uunet!decwrl!sdd.hp.com!uakari.primate.wisc.edu!ames!uhccux!robin
From: robin@uhccux.uhcc.Hawaii.Edu (Robin Amano)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Where is the power?
Message-ID: <8837@uhccux.uhcc.Hawaii.Edu>
Date: 2 Aug 90 17:55:01 GMT
References: <9759@discus.technion.ac.il>
Reply-To: robin@uhccux.UUCP (Robin Amano)
Organization: University of Hawaii
Lines: 16

In article <9759@discus.technion.ac.il> dario@discus.technion.ac.il (Dario Ringach) writes:
>Can anyone be kind enough as to explain me how can a mechanical mouse
>work when there is no Vcc pin assigned to the 9-pin D-connector on the
>IBM-PC serial interface?  Thanks in advance for any help.  --Dario.
>


I don't know how a mouse is actually wired, but if it needs power it's probably
getting power from pin 4 (DTR) or 7 (RTS).  When you turn on a serial port or 
any terminal (in most cases) DTR/data terminal ready and RTS/request to send
goes high, although I've seen some with only one of them high.  It usually will
stay high unless you are using hardware handshaking / ready busy.  On a 9 pin
4 = DTR, 7 = RTS / on a 25 pin 20 = DTR, 4 = RTS.  Also on some or at least 
most serial cards I've seen you can move around jumpers on the card to make
certain pins high.  You can check it with a volt meter, on a 9 pin 5 = gnd
on a 25 pin 7 = gnd.