Sega Mega Drive 27c040 EPROM

[xIceMan]

So,
I've been trying to burn 2x 27c040 EPROM to be used on a Mega Drive cartridge according to this page you are supposed to connect A0-A18 together to mask ROM
D0-D7 from 1st EPROM to D8-D15 on mask ROM
D0-D7 from 2nd EPROM to D0-D7 on mask ROM
CE and OE together to mask ROM
I've left Pin 1 floating and connecting it to 5V/BYTE won't make a difference.
However, it simply won't work.

I'm trying to burn the game Uwol Quest, which is a homebrew game. I've also byte swapped the file. No success. Am I doing something wrong? Does this 8Bit to 16Bit thing even work?
Help appreciated.

[Zorlon]

http://www.epforums.org/showthread.php?63960 might be worth looking at

P.S. have you had any working success with this with other games maybe retail games

It is worth trying other games outside of what you have tested to make sure it is working to start with

[xIceMan]

Haven't tried any retail games yet, at least not with 2x 8Bit EPROMs.
As for the guide you mentioned. I've already made carts with 27c322 EPROMs and they work fine. However, I ran out of EPROMs and shipping takes some time so I was tempted to try another method. Sadly without any luck yet.

[Jazzmarazz]

So,
I've been trying to burn 2x 27c040 EPROM to be used on a Mega Drive cartridge according to this page you are supposed to connect A0-A18 together to mask ROM
D0-D7 from 1st EPROM to D8-D15 on mask ROM
D0-D7 from 2nd EPROM to D0-D7 on mask ROM
CE and OE together to mask ROM
I've left Pin 1 floating and connecting it to 5V/BYTE won't make a difference.
However, it simply won't work.

I'm trying to burn the game Uwol Quest, which is a homebrew game. I've also byte swapped the file. No success. Am I doing something wrong? Does this 8Bit to 16Bit thing even work?
Help appreciated.

Alright, I made a picture for you.

Spoiler warning:

helpin the kids.png

One problem I see in your description is that you connected pin 1 to 5vBYTE, but both of those pins are inputs only. Ignore 5vBYTE and connect both ROM pin 1's (A18) together. This is the highest addressing bit, so it determines the bank of ROM that is being addressed. You must pull this pin either high or low. Either one is fine.


The other problem is that I do not know how you're programming your eproms. What programmer are you using? Are you burning them one after the other, or are you burning them as one ROM chip together? Since the process of writing to the chips will be done as 8-bits to ROM 1, 8-bits to ROM 2, 8-bits to ROM 1, 8-bits to ROM 2, etc, They must be programmed as though it is one 16-bit ROM chip. Let me know what origrammer you hyave and how they are wired to it before I can help you.

The 27c040 is a 512KByte eprom and you have two of them, but you are ignoring A18 as an addressable bank, so I can only conclude that Uwol Quest is a 512KByte game. If it is larger, then you will need to wire it differently. Also, only after you have programmed them and inserted the ROMs on the board, you must pull /WR high so that it never goes into a write mode while playing.

[xIceMan]

Hmm, that makes sense. I'll try that method.
Also, I'm using a Willem Programmer 5.0E and I'm burning them one by one with swapped bytes, of course.
I've expanded Uwol to 512KB since it's originally 64KB or less, can't remember exactly.

[Jazzmarazz]

Doing it one by one is your problem then. The data becomes broken into the wrong locations and is therefore read back to the Console incorrectly.

Since there are two banks of data with a resolution of 8-bits each, the console must see them as one bank with a resolution of 16-bits.
Here is the way it needs to be programmed:

00000000_00000000
11111111_11111111
22222222_22222222
33333333_33333333
44444444_44444444
55555555_55555555

But it is being programmed like this:

00000000_33333333
00000000_33333333
11111111_44444444
11111111_44444444
22222222_55555555
22222222_55555555


Since the Genesis reads the data one line at a time, you can see that it is not getting it correctly.

What you are going to have to do is trick your programmer. Take note of the tWC and tWP settings used for the 27c040 and tell your programmer you are programming a 27c400. Change the tWC and tWP settings top match the 27c040 and then wire the two ROMs into the programmer like my picture above. By doing this, your programmer thinks it is programming blocks of 16 bits, rather than two blocks of 8-bits.

Just be sure to match up the pinout as you will on the cartridge PCB.

[xIceMan]

Oh, I see. I didn't know about that. I thought you could simply burn 2 EPROMs with the same file and connect all pins except D0-D7. Thanks for the information.

[mgear25]

Doing it one by one is your problem then. The data becomes broken into the wrong locations and is therefore read back to the Console incorrectly.

Since there are two banks of data with a resolution of 8-bits each, the console must see them as one bank with a resolution of 16-bits.
Here is the way it needs to be programmed:

00000000_00000000
11111111_11111111
22222222_22222222
33333333_33333333
44444444_44444444
55555555_55555555

But it is being programmed like this:

00000000_33333333
00000000_33333333
11111111_44444444
11111111_44444444
22222222_55555555
22222222_55555555


Since the Genesis reads the data one line at a time, you can see that it is not getting it correctly.

What you are going to have to do is trick your programmer. Take note of the tWC and tWP settings used for the 27c040 and tell your programmer you are programming a 27c400. Change the tWC and tWP settings top match the 27c040 and then wire the two ROMs into the programmer like my picture above. By doing this, your programmer thinks it is programming blocks of 16 bits, rather than two blocks of 8-bits.

Just be sure to match up the pinout as you will on the cartridge PCB.

Hi Jazzmarazz i have 1 27c322, i want programing a roms snes 16mbits or 8 mbits. How program this eprom? Needed bridges in willem programmer for the roms in pair o dispairs, these is before o after programming?

Pd. Sorry for my bad English


00000000_00000000
11111111_11111111
22222222_22222222
33333333_33333333
44444444_44444444
55555555_55555555

[Zorlon]

Hi Jazzmarazz i have 1 27c322, i want programing a roms snes 16mbits or 8 mbits. How program this eprom? Needed bridges in willem programmer for the roms in pair o dispairs, these is before o after programming?

Pd. Sorry for my bad English


00000000_00000000
11111111_11111111
22222222_22222222
33333333_33333333
44444444_44444444
55555555_55555555

Wrong section, wrong thread, please just create your own thread

Thread closed.