IBM 360 Model 50 information?

[Jon Elson]

On 03/28/2019 11:46 AM, Ken Shirriff via cctalk 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.
If you had a 360 instruction set, why would you implement a 
360 by an emulator?
It would be most common that a microcode emulator would be a 
quite different scheme, kind of implementing an RTL 
(Register Transfer Logic) in a "language".
>   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 :-)
>
Wow, what a project!  I think the only way to understand the 
microcode is to follow the signals through the ALD 
schematics.  A microcode programming manual would be of no 
use to anyone, as the microcode bit pattern was stored in 
the serpentine word-line traces of the control store 
boards.  360/50 and 360/65 used CCROS (capacitor-capacitor 
read only storage) where there were two word lines on one 
board, one driven and one grounded through a resistor, 
called drive lines and balance lines, respectively.  If 
there was a wide pad on the drive line opposite the pad on 
the bit line, that generated a 1 in the control store word, 
if the wide pad was on the balance line, you got a zero.  A 
very thin Mylar sheet separated the two boards, and pressure 
was applied by a pressure plate and foam pad.  So, a 
microcode change required a board master artwork to be 
changed and a new board etched.  Not a practical field 
operation. The only custom microcode I heard of in these 
models was for the National Airspace System for the FAA 
traffic control computers.  The variant of the 360/50 was 
called a 9020D display element, and the 360/65 variant was 
called the 9020E compute element.  So, somebody used the 
required documents for that project.

Oh, one other issue is the 360's had no FFs.  All storage 
elements were transparent latches, and they generally used a 
4-phase clock. All this is pretty well documented between 
the ALDs and the FEMM's for the particular model.

Jon