[LMH]More microcode fun...

[Daniel Seagraves]

Someone care to help me figure this out?

In case nobody has figured out what I am up to yet, I'm playing with
emulating the Explorer II at the microcode level.  I got bored of trying
this with the DEC KS10, so I figured I'd try the Explorer.

I'm trying to logic out how the IO system works.

O-Bus functional destinations 20-37 and 60-77 appear to be the interesting
ones.

DEST	WHAT
20      VMA
22      VMA-Start-IO-Read
23      VMA-Start-IO-Write
24      VMA-Start-Read
25      VMA-Start-Write
26      VMA-Start-Read-Unmapped
27      VMA-Start-Write-Unmapped
30      MD
32      MD-Start-IO-Read
33      MD-Start-IO-Write
34      MD-Start-Read
35      MD-Start-Write
36      MD-Start-Read-Unmapped
37      MD-Start-Write-Unmapped

60      VMA-Start-Transport-Read-0
61      VMA-Start-Transport-Read-1
62      "-2
63      "-3
64      "-4
65      "-5
66      "-6
67      "-7
70      MD-Start-Transport-Write-0
71      "-1
72      "-2
73      "-3
74      VMA-Start-Read-Unmapped-NUBUS
75      VMA-Start-Write-Unmapped-NUBUS
76      MD-Start-Read-Unmapped-NUBUS
77      MD-Start-Write-Unmapped-NUBUS

First, in the case of 20-37:
Is the named location (VMA or MD) where the data goes/comes from, or is it
where the address is/comes from?

Which bus does this deal with?  Is this the Explorer private bus, or is
it some kind of memory-mapped IO-Space like the PDP-11 has?

Next, 60-77:
Same question, is the named register the data or address?
What do they mean by "transport"?

Now, general stuff -

I gather the two-operand micro-operations (Add, etc.) get a source
from both the A-bus and M-bus - But which bus is used for single-operand
microinstructions?