Extending this for a hn61256 32K ROM

Have you ever thought about creating a version of this for a HN61256 (or larger) 32K Mask ROM? You're just about there with this one, but many people want to use a 32K or 64K EPROM with the HN61256 as well. Almost every pin is the same on the bottom except Vcc on the top right, which is moved up.

Many of the mask ROMs used this same strange pinout for their 16K and 32K mask ROMs, and many vintage users have been struggling with making adapters for years. If you wanted to extend your adapter and trial it, I'd be more than happy to help.

Hi, what systems use these ROMs?

The project sounds rather simple anyway, I might think about it, but have you considered doing it yourself?

(Not intending to be mean, just a suggestion to pick up KiCad as this looks very good as a first project!)

Hi, @SukkoPera!

Thanks for your reply. The TI Compact Computer 40, TI-74, and TI-95 all use this mask ROM (http://www.datamath.org/ROM_IC.htm#Mask%20ROM) for an in-console ROM, while the CC-40 also uses them for cartridges. Ironic is that the pinout is very similar to the Tandy 61256’s, but not exact.

I came across your site because of the excellent collection of adapters you’ve made available to the community!

I raised the issue for the 61256 for several reasons. Firstly, I saw you were centralizing a collection of these adapters in a single repository, and would love to keep it simple for people to find these. Secondly, since you’ve completed numerous other adapters, you’re more familiar with how the control pins usually function (OE, CE, etc.).

I also have some background knowledge about the address, data, voltage, and ground pins, but I’m completely clueless about adapting the other ones. I’m more than willing to assist in debugging the board and ensuring it works with the 74 and CC-40 if you’re willing to help take a stab at helping me figure it out.

I’m also fine with modifying existing KiCAD layouts to suit my needs. (Check out my own repository for a power supply board that I modified.) Some projects prefer working on their own designs more than others, so it’s best to discuss this with the repository owner like we’re doing now. :)

If you have an existing board that you suggest as a starting point for this project, I’m willing to begin working on it to adjust the pins. I can also learn how to branch it and try to propose a merge back to your repo (which I haven’t done before.). However, I’ll need some assistance, and I’d greatly appreciate it if we could use your repository as the final destination for the project so that we can keep these designs in one centralized location. Please let me know your thoughts on this. I’m all for learning! Thank you again for the hard work!

I think this deserves to be a separate project, since making a single adapter would make it a nightmare to configure and since anyway this is one of my oldest KiCad projects (it could actually be the first one I ever did, it was started in KiCad 4 for sure!) and now I would do things a bit differently...

... which in fact I did, here's what I came up with:

I have a few doubts about the CE/CS pins, since I found this datasheet and it points out that the active level of those pins is configurable at the mask level, so I'd need to know whether the particolar ROMs you want to replace are active-low or active high. Any idea?

@hexbus ? :)

Hey there - sorry, I've been busy with real life medical issues; my apologies!

Several years ago, my friend I rescued the long lost CC-40 schematics from a TI Engineer and scanned them and placed them in the public domain. This has the module port and all its signals included (defaults). I'm asking the developer of https://github.com/go4retro/HEXTIr if they know what the default levels are offhand and where they might need to be hooked up to, since I really don't know.

1983_CC-40-final_schematics_and_block_diagram.pdf

I do have all of TI's schematics for cartridges for ROM/RAM and EPROM pinouts. The pinout going to the CC-40 might have changed, but the name of the pins the chips connected to should not have:

ROM modules (61256):

One 61256: CC-40_ALC_Application_ROM_Module_Jan_1983.pdf

Two 61256: CC-40_2-16KX8_32Kx8_ROM_Module_Feb_1983.pdf

Battery Backed up RAM:

One 6116: CC-40_2KX8_8KX8_RAM_Battery_Module.pdf

RAM Cart:

Two 8K x 8: CC-40-two-8Kx8_RAM-module-1983.pdf

EPROM Example:

Two 2764s: CC-40_16K-eprom-cartridge_1983.pdf

I'm continuing to dig and might have some additional schematics.

Adding these - I forgot that I had these on an old 486, so I might as well put them out in the public; an old friend sent them to me. These should help immensely and be much easier to read:

(Combo 27512 and 62256 RAM): cc40m2ro.pdf

(6264 battery backed up RAM): cc40m8k.pdf

(6264 x 2 battery backed up RAM): cc40m16k.pdf

(27512 EPROM - probably what we want!): cc40mech.pdf

61256 regular cartridge pinout (what we've been trying to clone or figure out): cc40mmp.pdf

(2764 x 2 EPROM cartridge): cc40rom2.pdf

Thanks a lot for the documents. All evidence seems to point to CS being active-high and /CE being active-low. I will have to think about it.