6800 opcode $02

[Allison]

The 6800 indeed had HCF and while I forget the opcode
(not a regular 6800 user) it was real.  Basically if 
the opcode was encountered the chip executed bus cycles
and did nothing else till reset.  Story then was it 
enabled some level of factory testing of the die for 
the is it even alive test.


Allison

>
>Subject: Re: 6800 opcode $02
>   From: "J.C. Wren" <jcwren at jcwren.com>
>   Date: Tue, 30 Aug 2005 21:45:00 -0400
>     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>    I'd suggest finding a VHDL or Verilog implementation, and see if 
>that provides any insight.  Also, Google for '6800 undocumented opcodes' 
>(no quotes).  There are a number of hits.  Most seem to indicate that 
>the undocumented opcode (no value given) causes the processor to go into 
>a mode where there are no instruction fetchs, but the address bus runs 
>incrementing bus cycles.
>
>    --jc
>
>Scott Stevens wrote:
>
>>On Mon, 29 Aug 2005 17:53:59 +0100 (BST)
>>ard at p850ug1.demon.co.uk (Tony Duell) wrote:
>>
>>  
>>
>>>Does anyone know what Opcode $02 is on a Motorola 6800 processor. It's
>>>
>>>not defined in the data sheet, but I have a device which forces that 
>>>instruction onto the data bus in one of the test modes.
>>>
>>>Is it, by any chance, the infamous HCF instruction?
>>>
>>>-tony
>>>
>>>    
>>>
>>Hmm,  all the other $0x opcodes on the table are inherent instructions
>>that mess with the condition code register.  Looking at the order of the
>>bits in the instructions, I don't see an order that corresponds with
>>good old HINZVC (we were required to memorize this, the order of the
>>bits in the condition code register, in tech school)
>>
>>0a clears overflow (V)
>>0b sets overflow (V)
>>0c clears carry (C)
>>0d sets carry (C)
>>0e clears interrupt mask (I)
>>0f sets interrupt mask (I)
>>
>>The lower instructions defined are
>>06  Accumulator A to CCR
>>07 CCR to Accumulator A
>>
>>
>>Is there a bit-level 'Opcode Breakdown' reference for the 6800
>>processor, that defines bit field and gives clues to how the opcodes are
>>translated in hardware, like there is (it's an elaborate table and I
>>even have a machine language Textbook that drags you through it all on
>>an early chapter) for the 8086 processor?
>>
>>The good old 6800.  'Freescale' : bah!
>>
>>  
>>