[Coco] 6809 / General CPU question

jdaggett at gate.net jdaggett at gate.net
Thu Feb 24 18:31:20 EST 2011


It was documented but in a odd way. If you look at the programming manual at the end of the instruction set description there is RESTART or hardware reset. Executing that opcode ($3E) will set the I and F bits in the CCR, clear the DPR and fetch the reset vector. This is essentially what happens when one pushes the reset button or issues a $3E opcode.


-----Original Message-----
>From: Arthur Flexser <flexser at fiu.edu>
>Sent: Feb 24, 2011 2:45 PM
>To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
>Subject: Re: [Coco] 6809 / General CPU question
>A further interesting note is that this is a rare case where the 6809 is NOT
>emulated correctly by the 6309, presumably because Motorola did not document
>the $3E opcode.  In the 6309, it gets vectored to the 'illegal opcode'
>On Thu, Feb 24, 2011 at 1:02 PM, <jdaggett at gate.net> wrote:
>> Interesting note is the 6809 has a restart opcode. Issuing an opcode of $3E
>> will will force the processor to load the RESET vector and start execution
>> again.
>> hope this helps
>> james
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>Coco at maltedmedia.com

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