[cctalk] Re: undocumented instructions including HCF [was: System 360 question]

[Charles Anthony via cctalk]

>
>
> The idea of a command that would brick the system is popular.
> It may be possible, but it's very difficult to track down the details from
> FOAFs.
>

Not bricking, but breaking:

From multicians.org:

"The tape drives used on the GE-635
 were some of the first self
threading drives. As a result they needed an extremely long tape leader
before the "reflector spot" and this was a pain for MIT operators
 when loading the tapes onto
the IBM 7094  running CTSS
. Lee Varian
 wrote some tricky code,
and we put two load point reflectors on the tapes we shuttled between the
7094 and the 635. The 635 would only sense the farther-in load point; the
7094 would load to the early load point and then Lee's code would space it
way out and rewind back to the 635 load point. If we didn't find the right
label, his code tried three times and then deliberately broke the tape so
the operator would have to put on new load points at the correct places.
(You could break a tape on the '94 by putting it into high speed rewind and
then doing a reset data channel command, I suppose it's safe to reveal this
now.)"

-- Charles


X-Clacks-Overhead: GNU Terry Pratchett

[cctalk] Re: undocumented instructions including HCF [was: System 360 question]

[Fred Cisin via cctalk]

The IBM monochrome monitor could be damaged by putting it into an 
unsupported mode.



The idea of a command that would brick the system is popular.
It may be possible, but it's very difficult to track down the details from 
FOAFs.


--
Grumpy Ol' Fred ci...@xenosoft.com

[cctalk] Re: undocumented instructions including HCF [was: System 360 question]

[Doug Jackson via cctalk]

There was a "Killer Poke" on the commodore PET that would alter the video
horizontal output frequency, which had the effect of physically damaging
the video hardware as the high voltage was generated by the flyback
transformer.l and there was no regulation.

It's mere existence made my father paranoid about machine code
programming.   I was probably 10 at the time.


On Sat, 2 Nov 2024, 8:57 am Cameron Kaiser via cctalk, <
cctalk@classiccmp.org> wrote:

>
> > I had remembered the HCF as being a z-80 thing, so I searched for it.
> >
> > All I can find says it was 6800, not 6502.
>
> The NMOS 6502 has a number of undocumented lock-up opcodes. However, they
> arise
> as a consequence of its instruction decoder PLA and weren't intended for
> testing like the 6800 HCF. They were eliminated in the 65C02, though later
> versions add the STP opcode as an intentional way to halt the CPU until
> reset.
>
> --
>  personal:
> http://www.cameronkaiser.com/ --
>   Cameron Kaiser * Floodgap Systems * www.floodgap.com *
> ckai...@floodgap.com
> -- Eggheads unite! You have nothing to lose but your yolks. -- Adlai
> Stevenson
>
>

[cctalk] Re: undocumented instructions including HCF [was: System 360 question]

[Cameron Kaiser via cctalk]

> I had remembered the HCF as being a z-80 thing, so I searched for it.
> 
> All I can find says it was 6800, not 6502.

The NMOS 6502 has a number of undocumented lock-up opcodes. However, they arise
as a consequence of its instruction decoder PLA and weren't intended for
testing like the 6800 HCF. They were eliminated in the 65C02, though later
versions add the STP opcode as an intentional way to halt the CPU until reset.

-- 
 personal: http://www.cameronkaiser.com/ --
  Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckai...@floodgap.com
-- Eggheads unite! You have nothing to lose but your yolks. -- Adlai Stevenson