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28-pin 24-pin Function (normative)
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2 - Input D5
3 - Input D4
4 9 Input D3
5 10 Input D2
6 11 Input D1
7 12 Input D0
8 13 Input A0
9 14 Input A1
10 15 Input A8
11 16 M2
12 17 CPU /ROMSEL
13 18 CPU R/W
14 ? Vcc
15 20 CPU A14
16 21 CPU A13
17 ? CHR /OE
18 - Output D5
19 - Output D4
20 24 Output D3
21 1 Output D2
22 2 Output D1
23 3 Output D0
Code: Select all
28-pin 24-pin Function (normative)
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24 ? Input PA10
25 ? Input PA11
26 22 Output CIRAM A10
27 ? PPU R/W
28 ? GND
- On the Mapper 173 board, Pin 22 is connected to CHR A14. To deterministically be a 0 or 1 depending on $4101 D0, the Input PA10 pin must be connected to Vcc, and the Input PA11 pin must be connected to GND (or vice-versa).
- On the Mapper 036 board, Pin 22 is not connected to anything, but is reportedly always high but somewhat unstable depending on register values being written. This may be the result of a broken chip, as previously claimed, but I think it's the result of one of the two inputs being connected to Vcc, and the other floating but mostly picking up a high signal.
After that, there are still three of the 24 pins with functions to distribute: Pins 4, 6 and 23. Of the JV001's functions, we still have PA13, CHR /OE, and PPU R/W. I'm not sure what the JV001 would need them for, but that's how they are connected on the Mapper 172 board.
Please note that my designations of D0-D5 are from the chip's point of view. Because the Mapper 172 board connects the CPU bits in reverse order, D5 is D0, D4 is D1 and so on, and Mapper 036's CPU D4/D5 are the chip's D0/D1.