From: jcox@x102a.harris-atd.com (Jamie Cox)
Subject: Re: serial port problem
Nntp-Posting-Host: x102a.ess.harris.com
Reply-To: jcox@x102a.ess.harris.com (Jamie Cox)    
Organization: Harris Govt. Aerospace Systems Division
Keywords: serial port, powerbook
Lines: 41

In article <1qcq4gINN2q7@calvin.usc.edu> wls@calvin.usc.edu writes:
>
>
>A friend asked me to build a cable to connect an HP fetal heart monitor
>to a Maciontosh (SE/30).  No problem, sez I.
>
>...
>I wanted to demo it on my PB 170, it won't work!
>
>The PB has been used running ZTerm and kermit using both internal and external
>modems; so I don't think it's the powerbook per se.
>
>When I send a "^51" to the HP it responds with "^55^AA" -- a test of the serial
>ports.  It works on the SE/30; but not on the PB170.
>
>I thought that the SE/30 is connected to earth ground and so is the HP. So I
>connected from the chassis of the HP to the PW audio (ground) connector; still
>NG.
>
>Any thoughts?

Battery powered devices like the PowerBook are sometimes more sensitive to 
serial port weirdness.  I had trouble with connecting my Mac Plus to an HP 95LX
handheld.  Everything else worked okay on that port, but not the HP. (it runs
on two penlite batteries).  It turned out that the plus (by accident or by 
design flaw?) was putting a 4 volt bias on the serial port that was doing 
weird things to the HP (which has only 3v dc!).  The HP worked fine when 
connected to the printer port.  

Does your PB screen get dim or anything when connected to the device?  Have you 
tried using the printer port?

Good luck. 

--jamie


Jamie Cox  jcox@ess.harris.com | Phone:           1 407 633 5757 (work) 
Harris Space Systems Corp.     |                  1 407 723 7935 (home)
MS ROCK-2, 295 Barnes Blvd.    |The Macintosh Meeting and Drinking Society
Rockledge, Florida  USA        | "Speaking only for myself."
