[Simh] VAX 8200

[Bob Supnik]

There's an almost total lack of 8200 (aka V-11 or Scorpio) documentation 
on the web. I have chip pictures 
(http://simh.trailing-edge.com/semi/v11.html), and I think the chip 
specs (which won't help much) are in my archive at the Computer History 
Museum. Here are some things to be aware of:

1. The 8200, unlike other mid-range VAXes, does not have a console 
microprocessor. There is a basic console implemented in the microcode. 
It can boot a device via "boot block" booting (for example, the console 
floppy). Thus, it's more like the LSI-11/F-11/J-11 chips, which had a 
basic console in the microcode. The MicroVAX family dispensed with 
console processors and console microcode in favor of boot ROMs.

2. The 8200 has a patchable control store. This was used to avoid 
updating the microcode chips (five of them, all VLSI) for every 
microcode bug. When the system was finally stable and shaken out, there 
was enough patch space left to replace the CALL/RET mask processing, 
which initially used the compact-but-slow MicroVAX II algorithm, with a 
more 8800-like version based on case fanouts. This need not be 
simulated, except insofar as boot processing may try to load it.

3. The 8200 floating point chip, which was not optional, is essentially 
the same as the MicroVAX CPU and has the same POLYx bug.

4. The 8200 series was the only VAX to use the BI as a memory bus. In 
the 6000 series, the XMI/XMI+ was the memory bus, and the BI was used 
strictly for IO.

I've written to a colleague who ran the microcode project for V-11 to 
see if he kept any materials, but I'm not holding my breath.