[Info-vax] OT: Halt and Catch Fire

[glen herrmannsfeldt]

lists at openmailbox.org wrote:
> On Wed, 03 Jun 2015 20:39:34 -0700
> Alan Frisbie via Info-vax <info-vax at rbnsn.com> wrote:
 
>> On 06/02/2015 08:25 PM, JF Mezei wrote:
>> > Yeah, I know , "HCF, Halt and Catch Fire"  was an IBM 370 
>> > instruction in many "hacked" university documents.
 
> Does that mean somebody inserted this as a joke?

I do remember that there were some joke instructions in those days.
Though I only remember that they were for DEC processors.
 
>> > Seems to deal with the emergence of the PC in early 1980s
 
>> I have a ditto copy (remember ditto copies?) of an instruction list from
>> the 1960s which had "Halt and Catch Fire", supposedly for the IBM S/360
>> Model 69.
 
> I don't think there was a Model 69 but Glen is older than 
> I am and (usually) remembers better.
 
> Certainly there is no HCF instruction in the POPS for 360, 370, or later.
> Not sure what this is about. I have not seen and not heard of an IBM
> machine catching fire and they haven't had uptime problems since the mid
> 80s. Sounds like venus envy to me.

S/360 and successors don't have a HALT instruction. To stop the
processor, set the WAIT bit in the PSW by loading a new one with
LPSW, or from an interrupt new PSW.
 
> There were (are?) only 3 opcodes that began with H. If I recall two were
> floating point. I don't remember what the third was.

I don't usually think of them by their first letter. S/360 has a
HALVE instruction for floating point, HER and HDR, for short and
long floating point.  There is HIO, privileged Halt I/O instruction.

So many instructions have been added in ESA/390 and now z/ that I
might expect some to start with H.

>> I am sure that it was copied from an even earlier list for the IBM 1620,
>> but I don't have a copy.   That would have been in 1965. 
 
> Now that very well could be. But I could not find any HCF opcode in S/360
> and later doc.

Now that so few people do assembly programming, it isn't as much
fun to add such instructions.

-- glen