ROM image on a M27C4002?

[nebiun]

Hello! This is my first post.
I try to make a Sega Genesis Cartridge using an original PCB with a M27C4002 to replace the original ROM and fill a ROM image on it.
ROM image are that suitable for emulators (like Gens)
Is this possible?

[oompa loompa]

I try to make a Sega Genesis Cartridge using an original PCB with a M27C4002 to replace the original ROM and fill a ROM image on it

i don't think replacing the original rom with a 27c4002 is going to work because most carts don't use the same pin configuration layout (you'd be lucky to get a cart that does match the same pinout as a 27c4002). it is, however, possible to use a 27c4002 to run programs off of on the genesis if you were to wire a cart up yourself, matching appropriate address and control signals.

if you were to wire up your own, i wouldn't use a 27c4002 because those 16 bit eproms are rare and expensive ;D

ROM image are that suitable for emulators (like Gens)

only rom images that are in binary format (the roms that are in smd will have to be converted to work on your eprom)

[cdoty]

admin said:

if you were to wire up your own, i wouldn't use a 27c4002 because those 16 bit eproms are rare and expensive ;D

Speaking of the roms, do you know a cheap place to pick these up?

The Neo Geo MVS system uses them.

[oompa loompa]

if i were in need to buy some, i would go to www.mouser.com. the last time i was looking up 16 bit eproms, mouser had some in stock

[nebiun]

admin said:

I try to make a Sega Genesis Cartridge using an original PCB with a M27C4002 to replace the original ROM and fill a ROM image on it

i don't think replacing the original rom with a 27c4002 is going to work because most carts don't use the same pin configuration layout (you'd be lucky to get a cart that does match the same pinout as a 27c4002). it is, however, possible to use a 27c4002 to run programs off of on the genesis if you were to wire a cart up yourself, matching appropriate address and control signals.

if you were to wire up your own, i wouldn't use a 27c4002 because those 16 bit eproms are rare and expensive ;D

ROM image are that suitable for emulators (like Gens)

only rom images that are in binary format (the roms that are in smd will have to be converted to work on your eprom)

I've some (used) M27C4002 already, so price is very low ;D.
About the pin-out: it is a simple 1to1 "conversion" or I must know somethings else? I read some docs about Genesis ROM pin-out and I think I can make a wire "converter" between the EPROM and the SMD.
But I'm not sure if and how missing/present pins in PROM can be emulated or connected to EPROM.
Can you help me?

[oompa loompa]

you will need to get yourself a pinout diagram of the cartridge edge connector of the genesis, and you'll need the pinout of your eprom chip. what you do is match up all the address, data, and control signals.

the lowest marked address from the cartridge connector will go to the lowest marked address of the eprom, like A0 from the cartridge will go to A0 of the EPROM. there should not be an A0 on your cartridge diagram because it's wrong to call it A0 =P (it should be A1, that's why i said lowest marked address). Then work your way up to the upper addresses until you run out of address singals to the eprom, keeping in mind to match address signals accordingly (only for example: A1 goes to A1, A2 goes to A2, A3 to A3, etc).

Then connect your data bus. this should be easy, Data 0 will go to Data 0, D1 goes to D1, D2 to D2, etc. You can swap the bits around with whatever endian your eprom programmer deals with

You will finally need to connect memory control and power lines. Power: Vcc to Vcc, Gnd to Gnd. OE from the cartridge connector to E, or whatever signal enables the outputs to appear on the bus (you'll need to consult your datasheet). Then connect CE from the cart connector to your chip enable of your eprom. There may be a PGM or a VPP signal on your eprom, just connect these to VCC.

note: its not a 1 to 1 connection to the mask rom chip of the cartridge =P

[playdude]

I found this thread while looking for information on putting eproms into megadrive carts.

Ive got some 16bit eproms - m27c322, which are 42 pins to put some 2megabyte games on.
After tracing back the megadrive cartridge connector pinouts back to the game boards rom pinouts - I discovered the only difference between roms in released games and my eproms is that the eproms have two extra address lines. Ive tried leaving the address pins on the eprom unconnected (a19 and a20) and have tried leaving them in, and I still get nothing when trying them on the console.
Can anybody suggest what im doing wrong?

[jlf65]

playdude said:

I found this thread while looking for information on putting eproms into megadrive carts.

Ive got some 16bit eproms - m27c322, which are 42 pins to put some 2megabyte games on.
After tracing back the megadrive cartridge connector pinouts back to the game boards rom pinouts - I discovered the only difference between roms in released games and my eproms is that the eproms have two extra address lines. Ive tried leaving the address pins on the eprom unconnected (a19 and a20) and have tried leaving them in, and I still get nothing when trying them on the console.
Can anybody suggest what im doing wrong?

You can't leave address lines floating... they need to be pulled high or low (tied to power or ground). Depending on which way you pull them will determine where you need to put the data for the game in the EPROM... the best option would simply be to repeat the data as many times as would fit - for example, if the game is 256K, and the EPROM is 2M, repeat the game data 8 times to fill the EPROM.

[playdude]

Thanks for your quick reply.
Well ive been trying to put 2meg games on the roms - so the whole rom space will be used. Is it possible to have game data filling the whole eprom if two address lines are not being used? or will the game work if i connect the the address lines to either power or ground?

[oompa loompa]

An M27C322 is a very good eprom to use because it will just plug right into any regular sega genesis cart. The extra addresses on the memory can be connected to the more addresses on the cart slot if you want to play really huge 32mbit games like sonic 3d blast.

You can also tie them to a switch that can switch the address to hi or lo, so that you'll be able to play multiple games on your eprom

[playdude]

I have tried putting the eprom in a Sonic 3D blast cart - the board in that cart has connections for all the adress lines of the eprom, all in the right places already - the pinouts are identical.
But when I try playing the games on the console nothing happens, it's driving me nuts now.
The chips seem to be programming fine, verifying them comes up with no errors.
I just can't see what im doing wrong

[oompa loompa]

you might need to flip the odd and even bytes around. i dunno where you can download a utility to do this for you though

[jlf65]

I was going to say the same thing - if the bytes are swapped, it's just going to instantly hang. ;D

it would be pretty easy to do a python script to flip the bytes around.

[playdude]

I've sorted it now, thanks a lot, your suggestions really helped get me there.
I can now play some of those unreleased games on my console