Re: 6809 / 6702 puzzle

Date: Sun, 22 Apr 2012 17:23:32 +0200
Message-ID: <25825379.39831335108212456.JavaMail.www@wwinf3724>

Although the address range of $EFE0 .. $EFE3 does assume that the buffered address lines that go to the 6702 chip are used as Commodore 
have identified them on the schematics as active high and low chip selects! If I were them I may have lied of course... However, as the 
Waterloo language disk software only ever addresses port $EFE0, this point is somewhat irrelevant.

A great website incidentally.

A bit off topic - but would anyone be interested in an FPGA implementation of the SuperPET? I have already done an FPGA implementation of 
the Apollo Guidance Computer from the schematics (see,agcnorm). Documentation on the front page is a bit 
sparse so far but the VHDL source code is fully commented. I have also been working on an FPGA implementation of Clive Sinclair's Science 
of Cambridge MK14 (one of the first computers I cut my teeth on here in the UK) and the Vectrex games machine (the latter of which is 6809 
based). I have most of the VHDL components to construct the processor, memory and display - but will have to work on the 'disk' from 


> Message Received: Apr 21 2012, 07:14 PM
> From: ""André Fachat"" <>
> To:
> Cc: 
> Subject: Re: 6809 / 6702 puzzle
> > My understanding therefore is that the 6702 is addressed when the address
> > lines are 1110 1111 1110 00XX or $EFE0 through $EFE3. I would 
> > assume that any other reads will access non-existent devices and will
> > potentially return garbage (unless there are some data bus 
> > terminating resistors somewhere which would provide a known default data
> > bus value).
> > 
> > By looking at the schematics I am also led to believe that the 6702 should
> > be accessible from the 6502 processor (as the 6809 and 6502 
> > appear to be "next door to each other" in the schematic diagram and share
> > the address and data buses). This means that you should be able 
> That confirms my analysis.
> André
> -- 
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Received on 2012-04-22 16:00:05

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