Original Post

Hello guys I have a question concerning making a dev cart for VB,

First of all I’m really not an electronics expert here my issue,

As per David Tucker plan/schematics I made my own dev cart I made it twice completly and I’m totally sure that there is absolutely no short. I also use two 32pins EPROM (27c801 from ST) for making this cart. Now the thing is that I’m not too comfortable with Hi-low byte programming. That probably why I have a small issue to make this working. Just as an information I use a USTR eprom programmer which is offering the possibility to program Hi and Low byte eprom.

There is few things about this schematics
that im not sure first;

Lets consider that C(X) means the connector edge pin for VB cart.
And that E(1) and E(2) are eproms.

All my issues are regarding working with 2 EPROMS.
This should be correct for EP(1)
C(D0) to E(1)D0 and so on until C(D7) to E(1)D7.

How do I start with E(2) Do I solder (E2)D0 to C(D8) or to C(D15)? What is the order for the datapins on the second eprom (high). In other words
EP(2)D0 to C(D8)
EP(2)D1 to C(D9)
EP(2)D2 to C(D10)

EP(2)D0 to C(D15)
EP(2)D1 to C(D14)
EP(2)D2 to C(D13)

and last thing is about /OE and /CE pins Chip enable…

Do I connect

C(CE) to E(1)CE AND E(2)CE
C(OE) to E(1)OE AND E(2)OE
I think this would be correct but unsure…
C(CE) to E(1)OE and E(2)OE
C(OE) to E(1)CE AND E(2)CE

What about the DEMO game size and EPROM size? If demo is 1024kb do I take 2 27C801-1024kb or 2 27C040-512kb because of the Hi low …

and what is exactly hi byte low bytes programming is this about splitting EVEN and ODD bytes or splitting First half and second half of a file.

Thanks for reading this poor and exhaustive newbie question;)

Any other than David tucker schematics around for a 2eprom 32pins 27C801? dev cart for vb?

Kind regards


Post Edited (07-28-04 06:40)

4 Replies

Well acutually it seems that nobody is willing to help you out.
I understand your issue but I dont know the answer does anybody would like to give him small help? Some of you guys have done the dev cart schematics anybody willing to post new schematics for future users? let the intereset grow and share your knowledge.



Well then if you are starting your own company you probably mean that you know how to make dev cart. I would like to get your opinion on a previously posted question by me.

Ive made dev cart in the past for NES and Gamegear… they work great so I wouldnt say im a complete newbie to this but im clueless when it comes to work with TWO EPROMS and HI LOW BYTES…

Can someone explain me and give me and schematics example of anything working with 2EPROM…

I would also need more information about Hi low bytes programming what is it exactly? does even and odd bytes are separated in two files or first half and second half of a file is splitted?

How big my eproms size needs to be if my rom is 1024kbs or 512kbs.

Thanks to anyone who will answer


If your cart is the same as the EPROM one, the following should apply:

The 1st EPROM has its D0-7 going to D0-7 of the cart
The 2nd EPROM has its D0-7 going to D8-15 of the cart
All the CEs should be joined together
All the OEs should be joined together
All A? lines are as normal

The tricky thing is programming the chips. You need to split the ROM image into 2 files – upper bytes and lower bytes.
This can be done with some programs. I can’t remember their names.


00020406080A0C0E (ODD)
01030507090B0D0F (EVEN)

Sorry, can’t remember which goes in which EPROM. 🙁

Hope this helps. Haven’t actually made a cart myself. Ask the regulars in IRC EFnet #VirtualBoy for more help.

EDIT: For a 1024KB file, you would need 2 x 512KB chips.

Post Edited (08-03-04 05:56)

lameboyadvance has his (ODD) and (EVEN) labels switched:

Data: 0123456789

Even: 02468

Odd: 13579

Notice that the two files are each 1/2 the size of the original. Thus, the chips should each be 1/2 the size of the file.

If the chip is larger, the file (either even or odd) must be either padded to size, or duplicated enough times to fill the chip.

E.g. for a 512KB chip and a 64KB file, the file is split into even/odd files that are 32KB each. Each chip must contain 16 copies of one of the 32KB files. (32 * 16 = 512)

Or, to save time burning EPROMs, you could use my program called “padromvb.exe” included in the gccVB distribution. It knows how to fit “0xFF” data (padding) in between the data and the “header” in a VB ROM. Since an empty EPROM is actually filled with 0xFF’s, the programmer can just skip the padding, saving a lot of time. (Obviously, you pad the ROM, then split it.) Because of the way it works, it will even work on commercial ROMs, which you shouldn’t even have, much less put into an EPROM cart 😉

BTW, the even bytes (0, 2, 4, etc.) go into the chip attached to VB pins D0-D7 and the odd bytes (1, 3, 5, etc.) go in the D8-D15 chip.



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