IBM 360 Model 50 information?

[Curious Marc]

Which brings us to the real problem: we don’t have 360 Model 50 ALDs. Anyone has them?

Marc

 

From: cctalk <cctalk-bounces at classiccmp.org> on behalf of "cctalk at classiccmp.org" <cctalk at classiccmp.org>
Reply-To: Jon Elson <elson at pico-systems.com>, "cctalk at classiccmp.org" <cctalk at classiccmp.org>
Date: Friday, March 29, 2019 at 8:45 AM
To: Ken Shirriff <ken.shirriff at gmail.com>, <General at ezwind.net>, "cctalk at classiccmp.org" <cctalk at classiccmp.org>
Subject: Re: IBM 360 Model 50 information?

 

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