27 Apr
2008
27 Apr
'08
12:21 p.m.
This brings seeral questions about the hardware.
What is the state of CTS/ (clear to send active low) if the state of
the input is false it will never send. It effectively disables the
transmitter and can be used for hardware handshake.
Also the command instruction must have bits 0 and 2 set to enable Tx
and RX repectively. Typical command byte would be 35H or 37H.
Allison
Subject: 8251 troubles
From: dwight elvey <dkelvey at hotmail.com>
Date: Sun, 27 Apr 2008 08:23:09 -0700
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Hi
I've got a funny problem with a 8251.
I've been writing 8080 code and seem to have a strange
problem.
I initialize the chip in async mode. I have a light box on the
serial wire. It is initialized to both send and recieve.
I send one character to the 8251 and it passes it to the software
on the 8080 side. I display it on the 8080 side.
I then send another character to the 8251. Nothing happens.
It won't receive until I reset it.
None of the status lights change. I can see the data light flicker.
It could be a bad part but it just doesn't seem that it would
work once and then fail to work for the second character.
It just doesn't make sense.
Is there something I'm missing about the 8251.
Dwight
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