15 Jan
2017
15 Jan
'17
9:37 a.m.
On Sat, Jan 14, 2017 at 12:01 PM, Adrian Graham
<witchy at binarydinosaurs.co.uk> wrote:
Hi folks,
STC Executel fun continues and I'm at the point where I'm fairly sure code
is running but it's stuck in a tight loop waiting for something to happen.
The 8085A reference tells me a non-memory I/O is signalled by IO/M going
high while it puts the port number on the address bus (0xE3 to 0xE8 in this
case), 8 bits on the data bus and sets S0/S1 to be WRITE. If that's the case
then this machine in its current state doesn't do any non-memory I/O - IO/M
is the only signal that stays low. It's not a failed CPU since I have 3
different ones and they all do this.
In the EPROM binary dump you posted I see code that is doing IN and
OUT accesses to the following port locations:
IN $70
IN $71
IN $D0
IN $E3
IN $E7
OUT $71
OUT $B0
OUT $BA
OUT $BD
OUT $D1
OUT $E2
OUT $E3
OUT $E6
OUT $E7
OUT $E8
In addition there is a routine with builds an IN instruction routine
from a variable location on the fly in RAM and appears
to call that in
a loop from ports $B2 through $BA
L0F26: LXI H,$F280
MVI M,$C9 ; RET instruction opcode
DCX H
MOV M,C
DCX H
MVI M,$DB ; IN instruction opcode
PCHL
L10BD: LXI H,$F2AB
MOV A,M
ANI $3F
MOV M,A
L10C4: MVI C,$B2
CALL L0F26
LXI D,$F281
L10CC: CALL L0F26
ANI $0F
CPI $0F
JNZ L10EC
LXI H,$F2AB
MOV A,M
ANI $80
JNZ L10E6
MOV A,M
ORI $80
MOV M,A
JMP L10C4
L10E6: MOV A,M
ORI $60
MOV M,A
MVI A,$0F
L10EC: STAX D
INX D
MOV A,C
INR C
CPI $BC
JNZ L10CC
RET