(For the record: boards JF-23, -24, -25, -29, -37 without battery+PRGRAM; -27, -40 with)
I'm have this strong hunch that writes to $F003 are latched on (at least) two of the pins on the SS88006, and those pins are connected to the µPD775x /PLAY and /RESET pins ... CPU D2 through D7 are connected to µPD775x I0 through I5
From tracing pictures of the PCB, I was able to get half the SS88006's pinout:
Code: Select all
M2 -> | 01 42 | -- +5
CPUA12 -> | 02
CPUA13 -> | 03
CPUA14 -> | 04
PRGA16 <- | 05
PRGA15 <- | 06 37 | -> /START
PRGA14 <- | 07
PRGA13 <- | 08
PRG/OE <- | 09
PRGA17 <- | 10
?a18? <- | 11
CPUA1 -> | 12
CPUA0 -> | 13
CPUD0 -> | 14
CPUD1 -> | 15
CPUD2 -> | 16
?D3? -> | 17
R/W -> | 18
/ROMSL -> | 19
/IRQ <- | 20
Gnd -- | 21