EXP283 pinout
The first release of Based Loaded has a patcher IC labelled “EXP283” (shrink DIP42) that patches the game to make the NMI handler safely reentrant. Subsequent releases instead have the NMI handler detect reentry and return early.
It appears to do two things:
- Reads from
PRG ROM ADDRESS & $7FFF == $0180replace the byte with $60; this replaces alda $0573withlda $6073 - Reads from $6000-$6FFF return MMC1 PRG A15 through A17 on D4-D6.
NC ?? | 1 42 | -- +5V
NC ?? | 2 41 | <- MMC1 PRG A17
NC ?? | 3 40 | <- MMC1 PRG A15
NC ?? | 4 39 | <- MMC1 PRG A14
NC ?? | 5 38 | <- CPU A12
NC ?? | 6 37 | <- CPU A13
NC ?? | 7 36 | <- CPU A7
NC ?? | 8 35 | <- CPU A8
NC ?? | 9 34 | <- CPU A6
PRG RAM +CE IN -> | 10 33 | <- CPU A9
GND ?? | 11 32 | <- CPU A5
CPU D7 <> | 12 31 | <- CPU A11
CPU D6 <> | 13 30 | <- CPU A4
CPU D5 <> | 14 29 | <- MMC1 PRG A16
CPU D4 <> | 15 28 | <- CPU A3
CPU D3 <> | 16 27 | <- CPU A10
CPU D2 <> | 17 26 | <- CPU A2
CPU D1 <> | 18 25 | -> PRG ROM /CE OUT
CPU D0 <> | 19 24 | <- CPU A1
NC ?? | 20 23 | <- MMC1 PRG /CE IN
GND -- | 21 22 | <- CPU A0