HN61256 mask rom

[ewanuno]

hn61256.pdf

i have a drum machine (roland tr707) with this chip in it: hitachi HN61256, well, 4 of them actually

seems like its quite a quirky chip, with its programable CS line and selectable 4 or 8 bit modes.

i don't have any immediate plans to do anything with this drum machine, since it already has a nice eprom mod. but i thought i should share the information with you just in case.

[piersfinlayson]

Thanks. yes, a bit odd.
Not supported by the firmware today but fairly easy to add a new algorithm to support. Looks like the 4/8 bit modes were factory selected.

[ewanuno]

This chip is also used in a few other drum machines by roland, most notably the TR909 hihat and cymbal sounds.

i have seen them used with both active high and active low configurations for the CS (roland tr707), but i haven't seen any in the wild that were configured in 4bit mode.

up until now most people are using adapter pcbs to replace these roms with 27xx chips.

[electricwool]

if you can probe the CS lines, you can probably get it to serve the two roms at once using some logic for the CS to switch between a high and low bank. like serving a 32x2 = 64k rom. the switching logic seems to be able to be handled by an arduino