EPROM replacement for 28-pin 1 Mbit mask ROM

DarrenF

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I have a game with 28-pin 1 Mbit mask ROMs (831000) for sprite data (OutRun).

Is there a pin-compatible drop in replacement EPROM?
And before anyone suggests 27C301, everything I find on it says it's 32 pin.
 
27C301 will work, if you have the extra holes on the circuit board to support it. If you don't, then you'll need a 27C301 and a couple of sockets to wire up an adapter and plug it in.

Outside of that you are stuck with finding a blank 28 pin 1Mb OTP ROM which will be very difficult. If you do find one, will your programmer support it? Mine will. ;)
 
27C301 will work, if you have the extra holes on the circuit board to support it. If you don't, then you'll need a 27C301 and a couple of sockets to wire up an adapter and plug it in.

Outside of that you are stuck with finding a blank 28 pin 1Mb OTP ROM which will be very difficult. If you do find one, will your programmer support it? Mine will. ;)

Thanks.

I'm afraid the EPROMs are jammed together pretty tight. Not enough room for another 0.2" of EPROM length, unfortunately (0.1" maybe).

If I could find some 1Mb 28pin OTPs, I think I could figure out how to cobble together a little 32-to-28 pin adapter to program them as 27C301 (assuming the programming details are the same, and only the pinouts differ).

I was hoping for a way to program sprite ROMs to facilitate OutRun/Turbo OutRun conversions/deconversions w/o robbing mask roms from other boards. But it sounds like doing that, and programming a bajillion 27256s (the only other strapping option on the board), are the only feasible options.
 
I'm afraid the EPROMs are jammed together pretty tight. Not enough room for another 0.2" of EPROM length, unfortunately (0.1" maybe).

Or you could build some risers from perfboard, sockets and extension pins like I did here : http://forums.arcade-museum.com/showthread.php?t=243075

I made those specifically because I needed to replace a 28 pin mask ROM with a 32 pin EPROM just like you are.

Brian.
 
Or you could build some risers from perfboard, sockets and extension pins like I did here : http://forums.arcade-museum.com/showthread.php?t=243075

I made those specifically because I needed to replace a 28 pin mask ROM with a 32 pin EPROM just like you are.

Brian.

Seems like a fine idea, however see the attached pic which shows why this isn't feasible on OutRun.

There are two rows of four ROMs, with exactly enough room for one pair of legs (0.1") between them. If I try to fit a 32-pin device (as shown) it actually fits into the first pair of legs in the neighboring socket. So without some sort of vertical up/down alternation, 32pin isn't going to fit.

I'll see if I can figure out how to strap it for 27512 (not documented) and how to split the ROM files. If that works, at least it'll only be 16 EPROMs vice a whopping 32 of 27256 (which is documented).
 

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Could you not stack a "dummy" 28-pin socket
just to lift your 32-pin chip above the others ?

(...wouldn't be very pretty, but it should work.... )

Steph
 
(PLCC) 27c010 on a carrier board to make it work in an 831000 socket.

(DIP) 27c010 to 831000 board to program the above in a normal eprom burner -- just seat the carrier in the programmer adapter with the 3 extra lines temporarily connected. (Assuming you don't have a programmer to do PLCCs)

This shit's not that complicated.
 

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