[Coco] 6309/6809 opcodes with mixed 8/16 bit registers

[Mike Pepe]

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-
> bounces at maltedmedia.com] On Behalf Of jdaggett at gate.net
> Sent: Friday, November 23, 2012 6:14 AM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] 6309/6809 opcodes with mixed 8/16 bit registers
> 
> On 22 Nov 2012 at 20:55, Mike Pepe wrote:
> 
> > I could have sworn the HCF on the 6809 was $FF. I recall that if you
> > were to take a 6809, stick it on a breadboard, give it power and clock
> > it'll run the address bus test routine- the data bus should float to
> > $FF if it's not connected...
> >
> > Hm, I should (re?) try that. I'm certain I've done this before.
> >
> > -Mike
> 
> Mike
> 
> Wrong
> 
> The only possible opcodes on page one that could be the HCF are
> 
> $14
> $15
> $18
> $1B
> $87
> $8F
> $C7
> $CD
> $CF
> 
> The rest of the unused opcodes on page one mirror and existing opcode.
> 
> example:
> 
> $00 and $01 are negate
> $02 and $03 Negate/COM depending on the Carry bit state
> $04 and $05 LSR
> $0A and $0B DEC
> 
> and so forth for all the even odd pair from $00 to $7F. This is due to an
> incomplete decode of the opcode. That is the Least Significant Bit is left
out
> of the equation in those instances.
> 
> darn this discussion is rekindling the desire to reduplicate as much of
the
> circuit in logic within an FPGA. Started that a few years ago and never
> completed it as an attempt to understand how the logic might have been
> done.
> 
> james
> 

Yep, I can certainly verify this, I have a wire-wrapped 6809 I can dig up
and a scope to see what the outputs on the address lines are.

-Mike