This tutorial is a step-by-step guide on how to make your very own 32KB Sega Master System cartridge. The cost is quite low (if you have a programmed EPROM or you are able to program your own) - I payed around AU$8 in parts for one of my carts as made in this tutorial.
These carts have been tested on a PAL SMS 1 and a PAL SMS 2.
The good news is that the cartridges use a re-programmable EPROM, provided that you have the appropriate facilities (EPROM programmer and EPROM eraser).
This tutorial would not have been possible without the Sega Master System cartridge port connector pinouts as found one Maxim's page: http://www.smspower.org/maxim/docs/pinouts.html. Maxim's webpage is an excellent resource for all things that are related to the Sega Master System, and I would like to thank him for the amount of effort and time he has put into creating it.
After the step-by-step section, there is a pinout for the cartridge PCB.
1. You will need a 27C256 EPROM chip. In this tutorial, I use an ST Microelectronics 27C256B chip. If you are using your own EPROM programmer, ensure that the programmer is able to write to both the EPROM model and manufacturer type. This should be documented within the programming software that came with your programmer or with any relevant printed documentation.
2. You will need a Sega Master System cartridge. In particular, we are looking for a cartridge with a single chip on the board. This chip should be a wide-body chip with 28 pins. The printed circuit board that I have used so far is the model 171-5519. I have found the correct chip size and printed circuit board in AUS PAL versions of The Ninja, World Grand Prix and F-16 Fighter, all of which are fairly common. This tutorial should work with many other games as well.
3. You will need a 28 pin, wide body socket. However, I did not have any handy at the time and my local electronics shop had run out of stock. So, I used a 40 pin wide body socket instead.
4. Remove the two screws on the back of the cartridge. Inside you will find the cartridge circuit board.
5. Check that the board only has one chip on it, and that that chip is a 28 pin, wide body chip. There should also be a ceramic capacitor in the top left and an electrolytic capacitor on the right side of the board.
6. Carefully desolder the chip. I usually use a vaccum solder pump for this sort of thing, because it is quite quick but it is not always 100% reliable (ie. sometimes a point must be worked on more than once before enough solder is removed). Perhaps you feel more comfortable with desoldering braid.
7. Here you can see the front of the board with the missing chip.
8. You will need to cut off the bottom six legs of each side if you are using a 40 pin socket like me.
9. Here you can see the 40 pin socket with the 12 legs removed.
10. You may need to bend the ceramic capacitor in the top left hand corner to the left.
11. This way, the top of the socket has room to fit correctly in place.
12. If you are using a 40 pin socket like me, you may need to move the electrolytic capacitor in the middle right hand side of the board over a touch.
13. This way, the bottom of the socket has enough room to fit correctly in place.
14. Place the socket on to the front face of the board, so that the twelve legs that were cut off earlier are on the right hand side of the board (if you are using a 40 pin socket like me). The stubs of the cut off legs should not touch the surface of the circuit board (if you are using a 40 pin socket like me).
15. Here you can see the socket sitting in place from the back of the board.
16. Solder the socket into place.
17. If your EPROM has been used before, you will need to erase it. For my ST 27C256 EPROM, I set my erase timer to 10 minutes. The amount of time required to erase your particular EPROM might be different, depending on the manufacturer.
18. Program the EPROM with the (legal) ROM of your choice. In my case, I am programming a homebrew test program. I am using a TOP2007 general programmer, which is USB powered - quite convenient. However, I did have to install the latest software from their website in order to be able to program the 27C256 without errors.
19. Gently place the EPROM into its socket. You may need to gently change the angle of the pins, so that they align with the socket correctly.
20. Enjoy your cartridge.
21. You may also like to solder your EPROM onto the board directly, as shown above. If so, do so gently and make sure you apply the soldering iron to the legs of the EPROM for short amounts of time only. The disadvantage of using a soldered EPROM is that you can only really program it one time.
23. The advantage is that it can fit inside an old cartridge shell.
Cartridge PCB Pinout
If you are interested in the pinout of the IC socket compared to the Sega Master System port, then this photo can help you.
The IC socket shares the same pins for both the front and the back (of course) but the edge connector that mates with the actual Sega Master System has two sides. The front side has the even numbers from 2 to 50 and the back side has the odd numbers from 1 to 49. This pinout is of course only relevant to boards that have a single, wide body 28 pin ROM chip on them to begin with.
The front side is the one where the ROM chip faces upwards, and the face of the front points towards the front of the Sega Master System when inserted into the console.
As one can see below, the pinouts of the socket on the PCB when compared to the SMS cartridge port in light of using a smaller size EPROM (i.e. 32KB) works out very nicely, and no changes or rewiring are required.
EPROM CART FUNCTION
1 2 CART: !W; EPROM: VPP
2 33 A12
3 32 A7
4 31 A6
5 30 A5
6 29 A4
7 28 A3
8 27 A2
9 26 A1
10 25 A0
11 24 D0
12 23 D1
13 22 D2
14 19,20,21 0V
EPROM CART FUNCTION
28 1,35 5V
27 6 A14
26 7 A13
25 8 A8
24 9 A9
23 10 A11
22 11 CART: !M0-7; EPROM: !OE
21 12 A10
20 13 !CE
19 14 D7
18 15 D6
17 16 D5
16 17 D4
15 18 D3