8 May
2025
8 May
'25
2:06 a.m.
? Section 4 of the "2200 Systems Maintenance Manual" here:
...
...contains the theory of operation of the CPU.
Subsection 4.2 is the
"General Instruction Set Description." The BASIC interpreter is contained
Thanks! Exploring more through this reference..
Page 88 in the larger (filesize) version of that Systems of Operations
(last sentence):
"In a similar manner, the complete microprogram is written to produce the
desired results and then is stored in a 'hardwired' Instruction Memory."
Not sure why they put 'hardwired' in quotes, instead of just saying memory
address (unless, as someone earlier suggested, they just hadn't evolved up
to that terminology yet).
The instructions (from the table) seem to be 20-bit: most of the opcodes
are 5-bit, except branch instructions being 4-bit. The operand registers
are 4-bit.
Page 93, 4.3 first sentence: "As mentioned in 4.1, the BASIC Interpreter
contained in Instruction ROM is the important link between the user's BASIC
program and the machine instructions." This followed by a memory map of
RAM (for symbol tables).
Later, the BASIC tokens are referred to as "text atom" (apparently 96
tokens each with a 16-bit address pointer for handling). Like the IBM
5100 (and S/3 before it), the line of BASIC must be syntactically valid
before it is accepted/stored. Like the 5100 manuals, they use the term
microprogram and microcode (which I think in their usage, are equivalent to
what we today call machine code and instruction set).
Then Section 4.4.1 goes cycle by cycle on the startup sequence. The PDF
(for me) isn't searchable, so I'm not seeing reference to any "hot key"
to
enable any kind of built in monitor/machine code entry like the 5100 had.
Neat stuff!
On Wed, May 7, 2025 at 2:13 PM J. David Bryan via cctalk <
cctalk(a)classiccmp.org> wrote:
> On Wednesday, May 7, 2025 at 0:50, Steve Lewis via cctalk wrote:
>
> > But back on the original Wang question: I still can't find high
> > resolution images of it's CPU board. According to 1991 discussion here
> > on the 2200B, there is also mention of the system not really having an
> > instruction set, BASIC was all it could do since it was "hard
wired."
>
> Section 4 of the "2200 Systems Maintenance Manual" here:
>
> http://www.wang2200.org/docs.html
>
...contains the theory of operation of the CPU.
Subsection 4.2 is the
"General Instruction Set Description." The BASIC interpreter is contained
> in ROM providing 20-bit instructions that are executed by the hardware.
>
> The "Wang 2200 CPU schematics" here:
>
> http://www.wang2200.org/schematics.html
>
> ...show that the ALU is a single 74181, implying essentially a 4-bit
> processor.
>
> -- Dave
>
>