Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!harrier.ukc.ac.uk!has
From: has@ukc.ac.uk (H.A.Shaw)
Newsgroups: comp.sys.m6809
Subject: Single Stepping a 6809
Message-ID: <4267@harrier.ukc.ac.uk>
Date: 24 Mar 90 19:42:51 GMT
Reply-To: has@ukc.ac.uk (H.A.Shaw)
Organization: Physics Lab, University of Kent at Canterbury, UK.
Lines: 30


I am developing a micro-computer for teaching technician grade students at a
Technicial College here in Canterbury.  At the moment they use a single board
6502 based system with HEX keypad, 7-segment displays, cassette port, 2K RAM
and 4K Monitor ROM.  They hand assemble 6502 code to control various addons
that are available for the board, such as A/D and D/A boards, stepping motors,
strain gauges, a 5-axis robot arm, and even a set of traffic lights.
The micor-computer costs around 300 pounds each to buy, which is far to much
for what they provide.
I have designed and have a prototype replacement computer based on a 6809 with
8K RAM and 8K ROM, RS232 and lots of digital I/O lines.

That was the background, now the problem...
The 6502 system can single step through a program.  If a switch is thrown then
the registers are displayed after each instruction is performed, and a key must
be pressed to get the next instruction to be performed.  On a 6502 this magic
can be done by controlling the interrupt line from the SYNC output and writting
the right interrupt code.  How is this done on a 6809?  I assume that the BA
and BS outputs are used in some way, together with an interrupt input.  I have
been involved with 6809s for about 6 years now, but have never bothered with
the BA and BS outputs before.  Could someone please mail me with any answer
they might have since I do not often read this newsgroup (maybe I should).

	Ta very much,


Email: has@ukc.ac.uk                         | Howard Allan Shaw.
Phone: +44 227 764000 Extn: 3834             | Room 111A, Physics Laboratory,
                                             | The University,
                                             | Canterbury, England.  CT2 7NR