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From: kim@mips.UUCP
Newsgroups: net.micro.amiga
Subject: Re: more on serial port flow control
Message-ID: <545@mips.UUCP>
Date: Sun, 6-Jul-86 19:31:55 EDT
Article-I.D.: mips.545
Posted: Sun Jul  6 19:31:55 1986
Date-Received: Tue, 8-Jul-86 04:01:06 EDT
References: <85@scubed.UUCP>
Distribution: net
Organization: MIPS ... where RISC is a way of life
Lines: 29

> 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.

> Do any of you understand what is going on here?

Hmmmm ... pin 18 of the serial port (Amiga side) is listed as being
signal  INT2*  in Appendix-E of the Hardware Manual.  Since the signal
is an "active low" signal (the "*" in its name), I would guess that
with the plotter off (but connected), this line is being pulled down, and
is causing Interrupt2 to the processor to be asserted continuously.

With the plotter disconnected, the signal is most likely being pulled-up
(or at least floats high), and thus no rupt occurs.

I've no idea why your plotter needs its CTS hooked-up to INT2* to work
though.

/kim
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