RESET *

[WillMcD96]

What in the world is the MC6809's RESET( 62)'s function???

Also,PAGE1(16) & PAGE2( 17)

Thanks!!

Im still typing in tons of code.... !

Will

[David Linsley]

WillMcD96 wrote:
>
> What in the world is the MC6809's RESET( 62)'s function???
>
> Also,PAGE1(16) & PAGE2( 17)

Page1 and Page2 set the 6809 to another opcode table. Ie all the Branch
instructions are in Page0 (default) and the Long Branch are in Page1 (or
is it 2 cant remember) - the page indicates to do a short or long
branch.

Basically, the page opcode preceded the opcode from the page you want,
the page resets back to page0 after the instruction has been decoded.
You can of course say page1,page1,page1,page2,opcode to get an opcode in
page2 if you want! ie you can have as many page1 or page2 sequentially -
it doesnt matter how many.

Cant remember what RESET does, sorry.

Ooh, just found it on Graeme Kinns Dragon page:

http://www.grempc.demon.co.uk/dragon/info/undocops.txt

documents the 6809 undocument opcodes.

Hope this helps.

David Linsley STNC Ltd
dlin...@stnc.com Software Engineer
--------- http://www.stnc.com/ -----------
Bringing Information to People on the Move

[WillMcD96]

Thanks so much!

Will

[Steve Noskow]

In article <19981023112040...@ng125.aol.com>, will...@aol.com
(WillMcD96) wrote:

> What in the world is the MC6809's RESET( 62)'s function???

You got me and Motorola on this one. If you are saying 62 is the
opcode (decimal), there is no op code decimal 62 which is $3E. It is
unused. The hardware reset pin is #37, so I can't figure out what you're
looking at.

> Also,PAGE1(16) & PAGE2( 17)

Some instructions have a two byte opcode. Once you get 256
instructions (or thereabouts) you have used up all the combinations
available in one byte. You need another byte for an instruction. Long
branches and LDS & LDY start with $10 (16) and some compares start with $10
or $11.

IF you're assembling stuff, look at the op codes for these
instructions in you assemblies - or write some garbage instructions and
look at the opcodes that get generated just to see what the op codes are.

--
I know everything, except how to be humble...a.a..and... how to stop
e-spam. Sorry 'bout the address munge, but it has reduced it a bit. Use
snoskow1 at server email here in mot in the com domain.

[Alan DeKok]

In article <snoskow11wokso...@muc12-1.pgac.cog.nut.com>,

Steve Noskow <snoskow1...@liame.tom.com> wrote:
>In article <19981023112040...@ng125.aol.com>, will...@aol.com
>(WillMcD96) wrote:
>
>> What in the world is the MC6809's RESET( 62)'s function???
>
> You got me and Motorola on this one. If you are saying 62 is the
>opcode (decimal), there is no op code decimal 62 which is $3E. It is
>unused. The hardware reset pin is #37, so I can't figure out what you're
>looking at.

Opcode $3E is the unofficial RESET opcode. Yes, it does a reset.

There's also the unofficial HCF opcodes $15, $16, $17, $18, where
the CPU Halts, and Catches Fire. Not literally, mind you, but it does
go utterly bonkers.

Then there's STA immediate ($87), which doesn't work due to the
read-next-byte-at-PC feature of the 6809. The STX immediate ($97)
works, but only stores the low byte of X, and leaves the high byte
intact.

Most other opcodes are the same as their nearest legal relatives.
This is because the 6809 uses bit encoding for the instructions. So
$40 (COMA?) is really binary '0100000X', and is thus the same as $41.
(to pick a number more or less at random).

Alan DeKok.

[WillMcD96]

catch fire????

I will see if the emulator does it... :)

[David]

>Alan DeKok.

>
> There's also the unofficial HCF opcodes $15, $16, $17, $18, where
>the CPU Halts, and Catches Fire.

Does Halt and Catch Fire really exist???
I need information about the HCF!

Alan DeKok say: "unofficial HCF opcodes $15, $16, $17, $18"
But the opcode $16 are LBRA and the opcode $17 are LBSR.

Who says true???

[Alan DeKok]

In article <qisZ1.1608$iT1....@weber.videotron.net>,

That comes from too long away from the 6809. Let me double check my
reference.

$14 and $15 are HCF. Apparently they're for testing, and strobe the
address and data lines. Not good in a running computer.

Most other instructions do something related to their nearest
bit-encoded relative. Hmm... I wonder what $38 does?

The $10 and $11 prefix are self-referential, too. And since the CPU
is "executing" an "instruction", interrupts are disabled for that
"instruction". So: $10 $10 $10 $10 $10 $10 $10 $10 $10 $10 $10 $10 $12
is 14 cycle non-interruptable NOP.

Alan DeKok.