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View topic - Need help for w27c512 EEPROM, 32kb games and 28-pin cartridge(no memory mapper)

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  • Joined: 09 Jun 2021
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Need help for w27c512 EEPROM, 32kb games and 28-pin cartridge(no memory mapper)
Post Posted: Sat Jun 12, 2021 7:51 pm
Hi.

I want to start by apologising. I had an account here, but, given the casualties, I lost access to the email of this account and could not recover. Please, forgive me. Second, there are several threads on the forum about repro 32kb games. But since these threads are already old, I confess that I was a bit clueless to reopen the discussion of these threads. I even sent a private message to @wasup, because in his reply to one of those threads, he said that he managed to make cartridges using the same EEPROM that I use in my experiments (please, really forgive me,@wasup! I just didn't want to reopen very old threads, sorry to bother you).

I have a Winbond w27c512. My donor cart, is an Alex Kidd in Miracle World, 28 pins (one chip only, no memory mappers). I'm making my own EEPROM writer. It selects games from an SD card (interfaces with an LCD display) and writes the selected game into the EEPROM. To make my job easier, I only write games of maximum 32kb(as I understand, so I avoid the need of a memory mapper, am I right?)

My question is: how do I connect the w27c512 in this simple 28 pin cartridge?

PS*: w27c512 has the OE and the VPP in the same pin, pin 22.

I appreciate everyone's help.

Best wishes.
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Post Posted: Sun Jun 13, 2021 3:56 am
You will need to find the pinout of the Alex Kidd chip you removed and match to the pinout of your EEPROM chip. Using a multi meter and a schematic of the card edge pinout can help you find out what pins are what too. You may need to reroute some pins but sockets can make this much easier as it means you wont have to alter the pins of your EEPROM directly. OE will be your output enable/program enable line, check your chips datasheet to see if its active low or active high and that will tell you if you need to tie it to vcc or gnd. Its probably going to be tied to vcc to be honest, but always good to check.

Hope this helps
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Need help for w27c512 EEPROM, 32kb games and 28-pin cartridge(no memory mapper)
Post Posted: Sun Jun 13, 2021 9:06 am
128KB Cartridges with no mapper have the following pinout. From memory I believe 32KB cartridges have the same pinout, but don't quote me on that:


     -------o------
/WR |  1        28 | Vcc
A12 |  2        27 | A14
 A7 |  3        26 | A13
 A6 |  4        25 | A8
 A5 |  5        24 | A9
 A4 |  6        23 | A11
 A3 |  7        22 | /EXM2*
 A2 |  8        21 | A10
 A1 |  9        20 | /CE
 A0 | 10        19 | D7
 D0 | 11        18 | D6
 D1 | 12        17 | D5
 D2 | 13        16 | D4
GND | 14        15 | D3
     --------------


*Sega's naming convention. Signal goes low for memory accesses 0x0000-0x7FFF.
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Post Posted: Sun Jun 13, 2021 9:12 am
asynchronous wrote
128KB Cartridges with no mapper have the following pinout. From memory I believe 32KB cartridges have the same pinout, but don't quote me on that:


     -------o------
/WR |  1        28 | Vcc
A12 |  2        27 | A14
 A7 |  3        26 | A13
 A6 |  4        25 | A8
 A5 |  5        24 | A9
 A4 |  6        23 | A11
 A3 |  7        22 | /EXM2*
 A2 |  8        21 | A10
 A1 |  9        20 | /CE
 A0 | 10        19 | D7
 D0 | 11        18 | D6
 D1 | 12        17 | D5
 D2 | 13        16 | D4
GND | 14        15 | D3
     --------------


*Sega's naming convention. Signal goes low for memory accesses 0x0000-0x7FFF.


Yes, you can stick any 27C256 or 27C512 on a 32kb cart or 128kb cart with no mapper, they're a different PCB with the same pinout.

The 32kb ones are MUCH friendlier with their footprints for desoldering, the 128kb ones use TINY holes and solder bases.

I've used a variety of EPROMS with no issues - ST/ Mitsubishi etc - you can get OTP (one time progammable) ones as well.

Don't forget to concatenate the ROM up to fill a 512 if you use one (these hold 64KB)

Also there's a free 32kb cart PCB floating around (the files to get them made) but it's "untested" . Shells are a rip off too. You can only get them for the megadrive on the cheap
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Post Posted: Sun Jun 13, 2021 3:37 pm
IllusionOfMana wrote
You will need to find the pinout of the Alex Kidd chip you removed and match to the pinout of your EEPROM chip. Using a multi meter and a schematic of the card edge pinout can help you find out what pins are what too[...]



Sir., your guidance is very helpful. I will look into it immediately. Thank you very much. Best wishes.
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Post Posted: Sun Jun 13, 2021 3:42 pm
asynchronous wrote
128KB Cartridges with no mapper have the following pinout. [...]



Thank you very much for this pinout, Sir! I will be looking at this information about the low signal. Best wishes.
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Post Posted: Sun Jun 13, 2021 3:47 pm
Quote
Yes, you can stick any 27C256 or 27C512 on a 32kb cart or 128kb cart with no mapper, they're a different PCB with the same pinout.

The 32kb ones are MUCH friendlier with their footprints for desoldering[...]


It's a great information and will help me a lot. I will look into this 32kb cart PCB. Sir, thank you very much for your help. Best Wishes.
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Post Posted: Sun Jun 13, 2021 3:49 pm
Gentlemen. I will update you as soon as I have success in my experiment. Thank you very much indeed. You have helped me a lot with your wisdom. I'll be back as soon as I am successful. Thank you very much! best wishes.
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Need help for w27c512 EEPROM, 32kb games and 28-pin cartridge(no memory mapper)
Post Posted: Mon Jun 14, 2021 7:22 am
Thought I'd also post the pinout for 256KB cartridges (without mapper) in case someone asks about converting a 256KB cartridge:

     -------o------
GND |  1        32 | Vcc
 NC |  2        31 | NC
/WR |  3        30 | NC
A12 |  4        29 | A14
 A7 |  5        28 | A13
 A6 |  6        27 | A8
 A5 |  7        26 | A9
 A4 |  8        25 | A11
 A3 |  9        24 | A15
 A2 | 10        23 | A10
 A1 | 11        22 | /CE
 A0 | 12        21 | D7
 D0 | 13        20 | D6
 D1 | 14        19 | D5
 D2 | 15        18 | D4
GND | 16        17 | D3
     --------------
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