There are several chips connected to the Oki83 C154 or Oki80 C154 MCU:

• NEC UPD7004 C ADC
• 5128 XRAM external SRAM
• Oki6260 A IO controller
• 38256 EPROM (32k) in some cases.

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):

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