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There are several chips connected to the Oki83 C154 or Oki80 C154 MCU:
as far as we can tell, the MCU can communicate with each chip independently due to logic gates being present on some address lines. Any MOVX A,@DPTR or MOVX @DPTR,A instructions will talk to chips on the bus. The following table summarizes what lives where on the bus (note: all addreses are in HEX):
;:__Note__: 8XXX is unused in the ECU and is earmarked for RTP|
Some jumbled background info about this:
These are all the addresses that the ECU loads into the dptr. I'm thinking that the address itself can control which of the support chips (6260A, 5128, ROM) are enabled.
#0110Bh (0001000100001011)
#0110Eh (0001000100001110)
#01120h (0001000100100000)
#0112Bh (0001000100101011)
#0112Eh (0001000100101110)
#01150h (0001000101010000)
#01151h (0001000101010001)
#01152h (0001000101010010)
#01154h (0001000101010100)
#01160h (0001000101100000)
#011F5h (0001000111110101)
#02000h (0010000000000000)
#02001h (0010000000000001)
#02002h (0010000000000010)
#02003h (0010000000000011)
#02004h (0010000000000100)
#02006h (0010000000000110)
#0200Ah (0010000000001010)
#0200Bh (0010000000001011)
#0200Eh (0010000000001110)
#0200Fh (0010000000001111)
#04000h (0100000000000000)
#04001h (0100000000000001)
The logic chips control which peripheral IC the MCU is talking to.
The 74 HC04? is a hex inverter.
When the high nibble high bit is 0 (2000h-4001h), pin 22 of the UPD7004 C is low and vise versa.
M5128 Pin 18 (CE - chip enable) -> 74HC132 pin 8 (Out 3Y)
From this we can figure that the NAND schmitt trigger out 3 enables/disables the RAM chip. Where do inputs 3A +3B go?
74HC132 pin 9 (In 3A) -> 80C154 pin 25 (A8) -> 6260 pin 11 (??)
74HC132 pin 10 (In 3B) -> 74HC132 pin 5 (In 2B) -> 74HC04 pin 13 (in 6y)
74HC04 pin 12 (out 6y) -> 80C154 pin 9 (RST)
74HC132 pin 11 (4 out) -> R143 -> 74HC132 pin 1 (in 1A)
74HC132 Pin6 (2 out) -> 74HC132 pin 2 (In 1B)
74HC132 Pin3 (1 out) goes to 74HC132 pin 12 (In 4A)
74HC04 pin 13 (out 6y) -> 74HC132 pin5 (In 2B) -> 74HC04 pin 13 (in 6y)
74HC132 pin 13 (in 4B) -> IC13 Pin5
74HC04 Pin 2 (out 1Y) -> 74HC132 pin4 (in 2A)
74HC04 Pin 3 (in 2A) -> 6260A pin 24 (??)
74HC04 Pin 4 (out 2Y) -> R55 -> C55 ->
74HC04 pin 6 (out 3Y) -> D7004C pin 22 ??
74HC04 pin 8 (out 4Y) -> ADC board pin 5
74HC04 pin 10 (out 5Y) -> 83C154 pin 14 (P3.4)
6260 pin 20 -> ADC board pin 3
6260 pin 12 -> 80C154 pin 30 (ALE)
6260 pin 13 -> 80C154 pin 16 (WR)
6260 pin 14 -> D7004C pin 19
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