[Coco] 6809 / General CPU question

jdaggett at gate.net jdaggett at gate.net
Thu Feb 24 20:52:51 EST 2011

What ever.


-----Original Message-----
>From: Darren A <mechacoco at gmail.com>
>Sent: Feb 24, 2011 7:12 PM
>To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
>Subject: Re: [Coco] 6809 / General CPU question
>On 2/24/11, jdaggett at gate.net <jdaggett at gate.net> wrote:
>> 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.
>> james
>The $3E opcode is never mentioned in Motrola documentation. The page
>you cited in the programming manual is describing what happens when
>the RESET pin is asserted (Hardware Interrupt), just as the preceding
>pages describe the effects of asserting IRQ, FIRQ and NMI.
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>Coco at maltedmedia.com

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