SNES MAD-1 Piggybacker for 74LS139
author: ziggy587
2 layer board of 0.78 x 0.75 inches (19.7 x 19.0 mm)
Uploaded:
October 4th 2022
Shared:
October 4th 2022
Total Price:
$2.90
UNTESTED! But should work fine, since there’s not much to it.
This is a small adapter for a 74LS139 that mounts on the backside of a MAD-1 decoder. Use it to connect multiple (max 4) PROMs to the MAD-1.
0.8mm thickness is preferred for easier soldering, but 1.6mm thickness is probably fine.
74LS139 is SO16 package. C1 is 0.1µF in 0603 package.
Address 1 & 2 pads = Use jumper wire to connect these to the next two highest address lines from whatever memory you are using. For example, if you are using 27C801 then use address lines A20 and A21 (connect A20 to pad 1 and A21 to pad 2).
The needed address lines might be present on the MAD-1 socket, in which case adding the jumper wires will be easy and clean. There are variation on how to wire these pins and I didn’t want to complicate the design with jumpers, so I opted to use solder pads with jumper wires instead.
Aside from the pads that attaches to the MAD-1 pins, there is no copper on the bottom side of the board, so you shouldn’t have to isolate it from the cart PCB. You may need to trim the legs of components (such as caps or resistors) on the PCB for a better fit.
ROM /OE 1, 2, 3 & 4 pads = Use jumper wire to connect these pads to the /OE pins on your PROMs. Pad 1 goes to PROM 1 /OE pin, pad 2 goes to PROM 2 /OE pin, and so on.
The 74LS139 is wired as follows:
Pin 1 - To MAD-1 pin 4
Pin 2 - Address line 1 (e.g. A20)
Pin 3 - Address line 2 (e.g. A21)
Pin 4 - PROM 1 /OE
Pin 5 - PROM 2 /OE
Pin 6 - PROM 3 /OE
Pin 7 - PROM 4 / OE
Pin 8 - GND
Pin 9~15 - NC
Pin 16 - +5v
You can also use this adapter for ExHiROM, you will just need to wire it a bit differently. For example, if you want to use two 27C322’s, then wire it in the following way: The pad for Address line 1, connect to A22. The pad for Address line 2, connect to ground. Then for the PROM /OE pads, connect pad 1 to the OE pin of your second PROM, and connect pad 2 to the OE pin of your first PROM. If it doesn’t work, then switch the /OE lines.
UNTESTED! But should work fine, since there’s not much to it.
This is a small adapter for a 74LS139 that mounts on the backside of a MAD-1 decoder. Use it to connect multiple (max 4) PROMs to the MAD-1.
0.8mm thickness is preferred for easier soldering, but 1.6mm thickness is probably fine.
74LS139 is SO16 package. C1 is 0.1µF in 0603 package.
Address 1 & 2 pads = Use jumper wire to connect these to the next two highest address lines from whatever memory you are using. For example, if you are using 27C801 then use address lines A20 and A21 (connect A20 to pad 1 and A21 to pad 2).
The needed address lines might be present on the MAD-1 socket, in which case adding the jumper wires will be easy and clean. There are variation on how to wire these pins and I didn’t want to complicate the design with jumpers, so I opted to use solder pads with jumper wires instead.
Aside from the pads that attaches to the MAD-1 pins, there is no copper on the bottom side of the board, so you shouldn’t have to isolate it from the cart PCB. You may need to trim the legs of components (such as caps or resistors) on the PCB for a better fit.
ROM /OE 1, 2, 3 & 4 pads = Use jumper wire to connect these pads to the /OE pins on your PROMs. Pad 1 goes to PROM 1 /OE pin, pad 2 goes to PROM 2 /OE pin, and so on.
The 74LS139 is wired as follows:
Pin 1 - To MAD-1 pin 4
Pin 2 - Address line 1 (e.g. A20)
Pin 3 - Address line 2 (e.g. A21)
Pin 4 - PROM 1 /OE
Pin 5 - PROM 2 /OE
Pin 6 - PROM 3 /OE
Pin 7 - PROM 4 / OE
Pin 8 - GND
Pin 9~15 - NC
Pin 16 - +5v
You can also use this adapter for ExHiROM, you will just need to wire it a bit differently. For example, if you want to use two 27C322’s, then wire it in the following way: The pad for Address line 1, connect to A22. The pad for Address line 2, connect to ground. Then for the PROM /OE pads, connect pad 1 to the OE pin of your second PROM, and connect pad 2 to the OE pin of your first PROM. If it doesn’t work, then switch the /OE lines.