IBM 360 Model 50 information?

[Lawrence Wilkinson]

On 28/03/2019 17:46, Ken Shirriff via cctech wrote:
> I'm writing a S/360 Model 50 emulator that runs at the microcode level, in
> order to drive a Model 50 front panel accurately. I'm about 80% of the way
> there, but there are some microcode operations that I haven't figured out.
> So I figured I'd ask if anyone has obscure Model 50 manuals that aren't on
> bitsavers, or perhaps even the ALDs.
>
> I was surprised at how extremely different the microcode is from the 360
> instruction set. I've figured out a bunch of the strange
> micro-instructions, such as S47ΩE, which ORs the emit field into flags 4
> through 7. But there are many micro-instructions that still puzzle me,
> like F→FPSL4 which maybe a floating point shift left 4 and 1→BS*MB which
> does something with byte stats. So if anyone happens to have a Model 50
> microcode programming manual sitting around, please let me know :-)
>
> Thanks,
> Ken

Welcome to the club!

Do you only have the manuals from Bitsavers? So CLDs but no ALDs.

Yes, something that does a FP shift-left-4 will be related to the IBM FP
format normalisation and it should be possible to work out exactly what
from the context. It may do other odd things and not just what the
operation mnemonic shows, e.g shift left 4 + increment exponent + set
flag on overflow, or perhaps the opposite to de-normalise for
addition/subtraction (see CPL 115.)

You could also look through the diagnostic sections to see if the
operation is used in there - this may well give exercise special cases
of the operation and confirm exactly how it is meant to work. I had a
problem with the 2030 ALDs and CLDs not being the same version (I think
the microcode/CLD was newer) and this meant it would not work with the
circuitry I had. I can't remember the differences, I think an extra
diagnostic latch or two, but once the diagnostics passed I was confident
they were correct.

Is there anything new at http://www.ibm360.info/ for you?

-- 
Lawrence Wilkinson                          lawrence at ljw.me.uk
The IBM 360/30 page                   http://www.ljw.me.uk/ibm360