Masked Rom Replacement Question

troxel

Well-known member

Donor 7 years: 2015-2021
Joined
Mar 19, 2006
Messages
2,084
Reaction score
104
Location
Lincoln, Nebraska
I believe I have a bad masked ROM on my Tumble Pop PCB. How do I know what is an equivalent ROM replacement? Looking at Ceaser, it looks like it would be a 27c512, but it's not 40 pin as the original masked ROM requires.

It's the map-00.rom gfx ROM that I want to replace.

Thanks again.
 

Attachments

  • tp.JPG
    tp.JPG
    69.2 KB · Views: 15
I don't know what the proper replacement is, but I do know you're mixing up bits and bytes when interpreting the size.

The list you posted (which is based on the MAME source) shows the image size in BYTES. And it is indeed 512kB (kiloBYTES). However, nominal EPROM sizes are NOT in kilobytes, but kiloBITS. 8 bits per byte, so you're looking for and EPROM that's 512*8=4069kb (kiloBITS). 27C040 are this size, but are 32 pins. Perhaps 27C4096 is what you want, it's 40 pins.
 
Thank you for the correction. Totally makes sense, and should help with finding a replacement.
 
DarrenF nailed it...

You need a 4M BIT eprom.

32 pin eproms are 27c040 or 27c4001 ( 8bit data bus)

40 pin eproms are 27c4096 or 27c4002 (16 bit data bus)


Hope this helps.

Steph
www.Hobbyroms.com
 
Back
Top Bottom