Space Invaders Single Rom Mod using 2764

orion3311

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Yeah - this question again. Found my old thread and looked at pins, read pinouts, etc. What

I don't get is, according to this..

http://www.coinop.org/kb_dl.aspx/KB/gametech/space invaders rom hack.html

I need only to connect pins 2, 23, and 24. Per the instructions no matter if its a 2764 or 28128 rom, it says to connect pin 24 to A14, yet the pinout shows pin 24 as A9 for all 3 (2716, 2764, and 27128). Does this mean it really should be connected to A14, or should I just leave it alone and only change pins 2, 23. (and 27/28 to +5v)

So long story short, in doing the single rom mod, does pin 24 stay connected to A9 or should it be connected to A14?
 
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Tried it both ways - neither worked. Get bars when both address lines are hooked up. If I leave A11 off it scrolls a bunch of blocks past. I am using a TMS2764 which unlike the TMS2716, is 100% compatible with regular 2764's.

Used hex editor to make the image starting with H. Should be ok??
 
I'm guessing that you have the Midway 2 board L-shaped boardset, in which case the following may not be helpful, or it MAY give you a few pointers .......... it's the info to hack the ROM board of a Taito 3-layer boardset so it only needs a single 27128:

Note: Do be careful with regards to the jumpers - if the board is strapped to take 2708's then you'll need to ensure that you don't accidentally fry your EPROM by connecting things in such a way that it receives -5 or +12 volts!

Space Invaders (3 layer) boardset - Single EPROM Hack (27128)

- The board that I took this from had the jumpers on the ROM board set to use 2708's (ie ensure especially that S2 and S3 are angled up and to the left and S5 to S8 go horizontally to the left). There should also be a jumper above the lowermost EPROM socket which goes across the lower two jumper pads (bottom left and bottom right) and underneath this socket the jumper should be across the top right and bottom left jumper pads).
- Remove all EPROMs from the ROM board
- Take a 28 pin DIL socket and bend out pins: 1, 2, 21, 22, 23, 26, 27, 28
- Plug this socket into the 24-pin socket at location IC31 (EPROM 6) ensuring that pin 14 of the 28-pin socket lines up with pin 12 of the 24-pin socket (therefore pins 1, 2, 27, 28 of the 28-pin socket hang over the top edge)
- Wire pin 1 to pins 27 and 28 and then connect to a +5VDC source (wherever is convenient)
- Wire pin 2 to S7 (3rd link up) - A12
- Wire pin 21 to S5 (5th link up) - A10
- Wire pin 22 to 3rd PTH up! - OE to GND
- Wire pin 23 to S6 (4th link up) A11
- Wire pin 26 to the fourth PTH up, just to the left of the 'S8' text - A13 (EPROM) to A14

NOTE: Make sure than pin 18 (by the original 24-pin socket numbering) is grounded, either via a cap just above EPROM socket location 31 or via a jumper above the socket !!!

Program a 27128 with the Space Invaders code. Merge the four binaries as follows:

copy /B invaders.h+invaders.g+invaders.f+invaders.e inv-27128.bin

Plug in the EPROM and power up!



BTW, your link goes to a currently unavailable page, here's the cached page:

http://webcache.googleusercontent.c...pace+invaders+single+27128&cd=5&hl=en&ct=clnk
 
You're right - I was looking at the wrong thing.

Either which way - tried again, burned a different 2764, still no go, exact same results. Not sure what the heck I'm doing wrong.

Board is strapped for 2716.

Pin 23 (on 2764) for A11 connected A11 @ S6
Pin 2 connected to A12 @ S6
Pins 27+28 connected to +5v
 
Tried Boot Hill on another 2764...this time the screen kinda draws white, then black, and just loops like that, almost like a window shade. Something tells me I'm burning the roms wrong.

basically using copy /b file1+file2+file3+file4 final.bin

Starting with H as the first file.
 
GOT IT!

Had to ground pin 20 (chip enable). I sat here thinking about it and why it would or wouldn't work, and I got to thinking as to how exactly the board would be able to read the program off of one chip vs 4 seperate chips, so I looked at the chip enable pin (pin 18 on the 2716 or 20 on the 2764). The address lines a11, a12, and a14 go into a decoder which then individually enables each rom chip normally. Whats happening is by hooking up the extra address lines directly to the larger rom, you don't need that chip to enable each physical rom, but with pin 20 connected its still trying (thus never letting it load completely (hence the looping), so simply grounding pin 20 does the trick.
------------------------------------------------------------------
So, here it is, in writing, the elusive single chip mod for regular Space Invaders to run on a 2764:

(Burn 2764 by combining all 4 Space Invaders roms into one, with H being the first and then the rest). If using dos prompt use copy/b rom.h+rom.g+rom.f+rom.e invader.bin.)

(Note: A TMS2764 is useable, unlike the TMS2716 which is different from a normal 2716).

Step 1: Strap the board for regular 2716's, but leave S2 open (regular = NOT TMS2716)

Step 2: Seat the 2764 into a 28 pin socket

Step 3: Fold pin 27 over to pin 26 and solder carefully. Fold pin 28 over and solder to 27, so that pins 26,27, and 28 are all connected, and pin 26 can still connect to the other socket. (THIS IS FOR THE 2764 ONLY, as pin 26 (normally vcc) is not connected and can be used to feed vcc to the new chip). 27128's and 27256's are different!

Step 4: Bend out pins 23 and 20.

Step 5: Seat 28 pin socket into 24 pin socket, with the bottom edge lined up so that the top 4 pins hang off. (really only pins 1 and 2 after folding 27 and 28).

Step 6: Connect pin 23 to A11, which is the jumper closest to the roms at S6. You can also choose not to bend out pin 23, and just connect A11 directly to the S2 jumper, which goes to pin 23.

Step 7: Connect pin 20 to ground

Step 8: Connect pin 2 to A12, which is the next jumper over from A11 at S6.

Step 9: Double check your work!

Fire it up and enjoy!
 
Very nice man... If and when I ever get my SI test station up and running this post is first on my list. (I think it was you who hooked me up with everything to make that station as well.)

Thanks...
 
orion3311- can you snap a couple photos? I think a photo would definitely help me visualize your write up. If possible, can you show your strapping, the 2764, and any jumpers?

Theron
 
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There's another active thread "Space Invaders Deluxe" by Kevin Mullins with a lot of detailed discussion regarding the strapping, but right now I have a board modded with just clip leads. Once my 28 pin sockets come in I'll get some pics. If you read it step by step though it'll make sense.

The only thing that may be confusing to some is the S6 jumper. Its near the middle of the board, closer to the roms. It looks like 3 little loops of wire, or some older boards it'll just be 3 angled traces parallel to each other. With the board on a bench and the daughterboard to the left, the jumpers are (left to right) A14, A12, and A11.
 
Ask and ye shall receive (much later)

As a little update to this - while my previous instructions (below) worked perfectly, the rom chip *should* have VPP (pin 1) connected to +5v. To accomplish this cleanly, I simply bent in pin 1, and use a resistor leg soldered to the bent-over legs (pins 28 and 27). You don't have to worry about the leg sticking down since that part of the socket hangs over the 24 pin socket anyway, just so long as it doesn't touch the board at all it's fine. Note that soldering this leg on takes some patience and needlenose pliers since the leg heats up enough to solder both ends at once (whether you like it or not).

The nice thing about using this folder-over-leg method is that it in the end, you only have to connect 3 actual wires to make this work (using a 2764).

Again, this is for a 2764 or TMS2764 ONLY. 27128 and other chips have different pinouts!

Pics attached!

So, here it is, in writing, the elusive single chip mod for regular Space Invaders to run on a 2764:

(Burn 2764 by combining all 4 Space Invaders roms into one, with H being the first and then the rest). If using dos prompt use copy/b rom.h+rom.g+rom.f+rom.e invader.bin.) Note: A TMS2764 is useable, unlike the TMS2716 which is different from a normal 2716.

Step 1: Strap the board for regular 2716's, but leave S2 open (regular = NOT TMS2716)
Step 2: Seat the 2764 into a 28 pin socket

Step 3: Fold pin 27 over to pin 26 and solder carefully. Fold pin 28 over and solder to 27, so that pins 26,27, and 28 are all connected, and pin 26 can still connect to the other socket. (THIS IS FOR THE 2764 ONLY, as pin 26 (normally vcc) is not connected and can be used to feed vcc to the new chip). 27128's and 27256's are different!

Step 4: Bend out pins 23 and 20.
Step 5: Seat 28 pin socket into 24 pin socket, with the bottom edge lined up so that the top 4 pins hang off. (really only pins 1 and 2 after folding 27 and 28).
Step 6: Connect pin 23 to A11, which is the jumper closest to the roms at S6. You can also choose not to bend out pin 23, and just connect A11 directly to the S2 jumper, which goes to pin 23.

Step 7: Connect pin 20 to ground
Step 8: Connect pin 2 to A12, which is the next jumper over from A11 at S6.
Step 9: Double check your work!

Fire it up and enjoy!
 

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Yes but it's a little different from the detail above. You can't use the folded-over leg trick because pin 26 does something else on those.

27C128 is like a regular 27128, the difference is that its an eeprom, meaning the burner can erase the chip rather than needing a UV light to erase it.

Here's a writeup on it although I haven't tried this one yet:

+---------------------------------------------------------------------------.
Space Invaders multigame (by Brendan Keith)
-------------------------------------------
Another fun way is to burn all 4 or 5 images into a 27128 or larger and
simply add 4 leads or so to the address jumpers. No cuts needed.

I started with a Bally Space Invaders board. S6 ROM jumpers were set to
AD11->a, AD12->b, AD14->c

I then took a 27256 and burned in both the Space Invaders set and Space
Invaders Deluxe. I can do this because I own both boards so don't anyone
try to get smart. The ROM set has to be merged and burned in with the H ROM
lowest and the higher segments filled with whatever to make up two full 16K
blocks.

This new ROM can be plugged in to any of the ROM sockets but sockets F and
G are closest to the jumpers that we need to connect to. Plug it in with
bottom pins lined up. The top 4 pins hang out.

Now for the jumpers. They are really quite simple. I used a 28 pin socket,
bent out the following pins and soldered wire wrap wire to the legs. The
socket itself can then be plugged in to the existing ROM sockets.

Pin 1 to GND
Pin 2 to AD12->b jumper.
Pin 20 to GND
Pin 22 to GND
Pin 23 to AD11->a jumper
Pin 24 to AD14->c jumper
Pin 27 to the center pole of a switch between GND and +5 to switch games.
Pin 28 to +5
 
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Yes but it's a little different from the detail above. You can't use the folded-over leg trick because pin 26 does something else on those.

Pin 26 is just the high address line on the 27128 (and nothing on the 2764), so you can do the exact same instructions as above and it will work. Just make sure the code is burned into the top half of the 27128 (it won't hurt to have it in the bottom as well, so just double-up the image and burn it).

27C128 is like a regular 27128, the difference is that its an eeprom, meaning the burner can erase the chip rather than needing a UV light to erase it.

No.... 27C128 is just the CMOS version, not an EEPROM.
 
My bad I can't remember all these friggin letter and number combos lol.

If you say it'll work I'll take your word for it, in fact I could even try it to see what happens.
 
what i would like to know is?

when you type copy /b (i was using windows dos) it copied the inv bin (merged) but,where was it?i dont know the location of this rom now.what directory is /b?

why do i get the idea it was supposed to be the letter of my harddrive in my case c?
:)
 
/b is the option for binary copy when appending files.
In the example above, the destination file would simply end up in the current working directory.
 
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