Well
I have some good news & bad news Gary.
Quite
by accident and for other reasons, I popped the 80386 board
into my test system using the Cyix 80486-40 rather than the
normal AMD 80486-40. To my surprise I found I could not
get the SMB V2 with K4 (2-3) i.e. output a bit 0 to a 1 to
switch in the 80486.
If
you remember the Cyrix is a poor man’s 80486. It’s an 80486
(without the math processor) in a 80386 socket. It runs
80386 code about 10% faster.
What
is interesting is that the old SMB V2 K4 1-2 position
switched fine and back to the Z80. Removing the K4 and
using the Cyrix P32 1-2 & 3-4 also worked fine back
& forth.
As
Shakespeare said: Something is rotten in the state of
Denmark here. I suspect the problem may be on the SMB
V2 port and not the 80386 board.
There
were some 74Fxx chips on the Cyrix board that were not on
the AMD board (have two BTW, both behave the same), I
switched these – no difference.
It’s
late, so more tomorrow – the goes my weekend!
On
yours BTW, remember the SMB V2 LEDs are not monitoring the
actual S100 bus lines, they are looking only at the output
of the FF, U33. Also remember you are seeing Q* and not Q.
The front panel “TMA” LED however does show the S100 bus
status of TMA0.
In
any event your TMA3* should never light up. This indicates
that pin 3 of U33 is going low. My BIOS for MSDOS for the
8086 family uses TMA0*
From
the MASTER.Z80 Monitor…
;
;THIS
ROUTINE ACTIVATES THE S100 TMA0* LINE USING THE SMB
(SWITCHES COMTROL OVER TO THE 8088, 8086 or 80286....)
;Inputting
(any) data from Port SW_DMA0 lowers the S-100 TMA0* PIN #55
line.
;THIS
WILL CAUSE THE 8086/80286 BOARD TO BECOME ACTIVE AND TAKE
OVER THE BUS.
;THE
Z80 WILL BE IN A PERMANANT HOLD STATE UNTIL THE S100 PIN #55
IS AGAIN RAISED.
;NOTE
FOR THE NEW V2 SMB WE RAISING BIT 0 OF PORT 0EEH (AND ALSO
LOWERS TMA0* FOR THE SMB V1 Board).
;WE
WILL INCLUDE BOTH OPTIONS
SWITCH_8086:
LD HL,MSG14
CALL PRINT_STRING
IN A,(SW_TMA0) ;THIS SWITCHES CPU'S with no block
Move
NOP ;Z80 WILL BE HELD HERE
NOP
LD A,01 ;Utilize the more specific circuit
on the V2-SMB
OUT (SW_TMAX),A ;Make sure its bit 0
NOP
NOP
JP BEGIN ;WILL DROP BACK TO REBOOT MONITOR
Hope
this helps. Will dig some more tomorrow.
John