Replace Console GROM on a cartridge for power up?

[Tator]

Hi everyone,

 

I've recently found some time to work on repairing a collection of non-working TI-99/4A consoles I've acquired over the years. While I have replacement RAMs and ROMs ready, I don't have any spare GROM ICs to replace faulty ones.

My question is: would it be possible to boot a console without the original GROM ICs by using alternatives through the cartridge port?

From looking at the schematics, it seems plausible that having the necessary ICs at the cartridge port might work. However, since I don't have those specific ICs, I wonder if using something like the FinalGROM (with GROM dumps loaded on an SD card) or a board like the UberGROM with the console GROM dumps would be a viable solution.

I believe it could work, but I'm sure there are experts here who can provide the right insights. As always, I greatly appreciate the support of the TI community.

 

Best regards,

 

Sebas

 

[Shift838]

Look into the GROMMY boards to replace your console GROMS.

[Tator]

Thank you, where can i order GROMMies?

 

 

[Gary from OPA]

24 minutes ago, Tator said:

Thank you, where can i order GROMMies?

 

 

You can connect with designer directly @speccery and I think in near future @arcadeshopper will be stocking them soon as well.

 

I have 4 grommy2's already, one in each one of my consoles, as not only can you use it to replace the console groms, it has more grom space, so it can also run my SOB, and I am working on releasing soon a powerful new v2 of my SOB for the grommy2.

[Tursi]

The answer to your original question, though, is yes. The GROMs all sit on a shared bus, so in the console, or in the cartridge port, they all work.

 

[+DuaneAL]

14 hours ago, Tursi said:

The answer to your original question, though, is yes. The GROMs all sit on a shared bus, so in the console, or in the cartridge port, they all work.

 

And through the expansion port as well? 

[Tator]

Would it be feasible to configure the FinalGROM to serve GROM 0,1 & 2 and the GROMS/ROMS for a certain cartidge i.e: TI Extended Basic and boot without the console GROMS inserted and with the FinalGROM inserted and be able to enter the initial screen and choose either TI-BASIC or the cartridge?

[HOME AUTOMATION]

As it stands the FinalGrom 99, will only place GROM images, at >6000 - >FFFF. A small change in the firmware would probably allow lower addresses to be loaded.

As for removing every last real GROM IC, from the console ...Depending how the FinalGrom 99's, address incrementing works ...you might need to leave at least one.

[Tursi]

7 hours ago, DuaneAL said:

And through the expansion port as well? 

I haven't tested that, but if you can decode the GROM bus, then yes.

GROMs have internal addressing, so there's no address map in the hardware for them. Just two control lines and 8 data lines.

 

[Tursi]

4 hours ago, HOME AUTOMATION said:

As it stands the FinalGrom 99, will only place GROM images, at >6000 - >FFFF. A small change in the firmware would probably allow lower addresses to be loaded.

As for removing every last real GROM IC, from the console ...Depending how the FinalGrom 99's, address incrementing works ...you might need to leave at least one.

Yeah. I tested the UberGROM with all console GROMs removed and it worked fine (from the cartridge port). Unfortunately, I didn't appear to save the code with address read-back working. You need at least one real GROM to provide that if the hardware attached doesn't.

 

Unfortunately, with even one real GROM on the bus, all GROM accesses slow down to their rather poor access speed.

Fortunately, GROMs aren't accessed often enough for this to be really noticeable. With my UberGROM test I speed-tested a FOR loop in TI BASIC and even though the UberGROM is roughly 3x faster than real GROMs, there was no measurable benefit in TI BASIC over a 1 second test.

 

[Gary from OPA]

4 minutes ago, Tursi said:

Yeah. I tested the UberGROM with all console GROMs removed and it worked fine (from the cartridge port). Unfortunately, I didn't appear to save the code with address read-back working. You need at least one real GROM to provide that if the hardware attached doesn't.

 

Most of the gram and grom emulators out there, never did GROM read-back address, so you always needed one real grom in the system, even with my POP-Cart and SOB, so far only the grommy2 from @speccery does a true full emulation with address read back as well. -- The unicorn design for 99/22 does as well, so it can replace all original console groms, but there is still some issues with it with it co-existing with other devices that use the cartridge port as well.

 

As for outside expansion port on sidecar, yes you can run groms there if you decode the address bus, that is how the HSGPL and PGRAM and Gram-Krate cards work in the PEB, and how the PicoW Sidecar project by @JasonACT does it, which can also override the console groms, i am not sure if he does grom address read back, i never tested it with all 3 console groms removed.

[JasonACT]

7 hours ago, Gary from OPA said:

i am not sure if he does grom address read back, i never tested it with all 3 console groms removed.

Nah, I don't, there's a comment in my code that says I rely on the console GROMs.  I could do it, but the Pico with Arduino environment doesn't boot fast enough to emulate the >0000 console GROM (there's a lot of C++ library class initialisation before main()) to be ready in time at first power-on, so no point with my device.

[apersson850]

Back in the days you could use the GRAM kracker to override the console GROM chips. The GRAM kracker simply drove the bus harder than the standard GROM chips. Shout louder and you can't hear people talking.

[speccery]

On 11/7/2024 at 2:31 PM, apersson850 said:

Back in the days you could use the GRAM kracker to override the console GROM chips. The GRAM kracker simply drove the bus harder than the standard GROM chips. Shout louder and you can't hear people talking.

This feature is also supported by my strangecart project, but I haven't recently tested it since I don't want the strangecart and grommy2 to be pushing against each other, that would be a different competition of drive capability than the stranegcart agains GROMs, where the GROMs lose. In my test system I have grommy2 permanently installed.

Edited November 8 by speccery