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PROG-BK1 27C160 bankswitching 32Mbit (4MiB) workaround

pierpa86

pierpa86

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Hello Guys :)
Experiment time !
Looking online I found a user online who used this very interesting technique which allows you to make a stack of 27C160 to obtain a 32Mbit (4MiB) V rom.
It appears to be using the PCM-A20 pin that is normally used to enable the 16Mbit (2MiB) banks as the CE pin of the primary and secondary LS139 chip.
Do you think the pin out of the second LS139 that I wrote is correct?
Original image here:
https://www.aussiearcade.com/upload...0488.jpg.143e32c5df41cab95f4f451c29c85535.jpg


Senza-titolo-3.jpg
 
yeah, it's a pretty old-technique to get double sized ROMs when no larger chip is available.

the biggest issue with this I think is the fact that stacking the 27c160s like this the PCB will no longer fit inside the plastic shell.
 
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twistedsymphony said:
yeah, it's a pretty old-technique to get double sized ROMs when no larger chip is available.

the biggest issue with this I think is the fact that stacking the 27c160s like this the PCB will no longer fit inside the plastic shell.
Click to expand...
I never do that, but i wanna try, i miss something in pinout ? i get the correct pinout ?
 
I don't know how this particular setup is wired but generally you'd need some AND and NOT logic gates to toggle the OE pins properly for selecting the correct chip.

so basically OE for lower chip is OE && NOT A21 and OE for upper chip is OE && A21
 
I know how V-ROM jumpers work,

That document doesn't tell you anything about how to bank switch piggybacked ROMs.

I'm not sure I fully understand what you're even asking me at this point.
 
I'm trying to understand the basic logic of progbk1
it seems that by default it was already using two data addresses to do bankswitching with ls139 so the pinout I wrote in the photo makes sense.
 
Here guys a little piece of italian modern art and some little guide point for everyone that will do piggy backing to have 4Mb VRom (32Mbit) using 2Mb 27c160 eprom.

1) Disconnect pin1 from GND on the first LS139 and connect it to PCM_A20
3) On JV3 take PCM_A20 signal also for the new LS04
Only V Jumper: JV6 + LV5 - JV7 + JV8 + JV9 +JV10


OK.jpg


All parts shown in photos were taken from puzzle bouble converted or other titles many years ago (including LS04 and LS139) no working games were killed for this conversion. :D
 
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Looks awesome, a great outcome and great persistence seeing it through to the end. Thank you for sharing you work
 
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