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Path: utzoo!watmath!clyde!caip!cbmvax!carolyn
From: carolyn@cbmvax.cbm.UUCP (Carolyn Scheppner)
Newsgroups: net.micro.amiga
Subject: Re: more on serial port flow control
Message-ID: <489@cbmvax.cbmvax.cbm.UUCP>
Date: Mon, 7-Jul-86 10:47:45 EDT
Article-I.D.: cbmvax.489
Posted: Mon Jul  7 10:47:45 1986
Date-Received: Tue, 8-Jul-86 06:42:03 EDT
References: <85@scubed.UUCP>
Reply-To: carolyn@cbmvax.UUCP (Carolyn Scheppner)
Distribution: net
Organization: Commodore Technology, West Chester, PA
Lines: 41

In article <85@scubed.UUCP> phil@scubed.UUCP (Phil Cohen) writes:
>I recently posted a note detailing my experience with flow control
>on the Amiga serial port.  I had to hotwire pin 5 on my plotter to
>pin 18 on the Amiga in order for the CTS handshaking to work.
>
>Last night I was working on the Amiga and not using the plotter
>so I did not power it on.  Guess what!  The machine would not 
>kickstart until I unplugged the cable going to the plotter.
>Turn the plotter on or unplug the cable and everything works fine.
>
>After the machine is up and running, you still need to power on the
>plotter or unplug the cable or whatever you are running will lockup.
>This is true even if the application does not use the serial port.
>Again, if I power on the plotter or unplug the cable all returns to
>normal.
>
>Do any of you understand what is going on here?
>
>Phil

   I'm not a hardware type but here's my guess.  Pin 18 of the Amiga's
RS-232 port is documented as INT2* (normally high interrupt line).
Your plotter's pin 5 must be normally high, going low when it's buffers
are full, stopping not just serial transmission but whatever else
runs off INT2.  When your plotter is off, it is not holding pin 5 high
and grounds INT2*, freezing PORTS (8520A, external2) interrupts.

   I don't think this a good place to connect your pin 5.  What are the
ready and not-ready voltages put out by your pin 5 ?  There should be
a way to hook it to the Amiga hardware handshaking lines (CTS/RTS).
You will have to disable software (XON/XOFF) handshaking and enable
hardware handshaking using a program like setserial or Beta 1.2
Preferences.


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Carolyn Scheppner -- CBM   >>Amiga Technical Support<<
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