ti-74 Module Question

[+dhe]

It would seem 8K modules for the TI-74 BASICalc are fairly common.

 

Modules like Pascal are not.

 

Doesn't anyone know if it's fairly trivial to sacrifice an 8K module and make a Pascal Module?

 

Or has someone created a superduper (multimodule) module for the TI-74?

[+Ksarul]

There was someone selling 128K or 256K TI-74 memory modules on eBay a few years ago. . .

[+acadiel]

We can likely design new ones.  From what Stephen Reid mentions, the bank switch code locations are static (you roll your own routines and put them in a specific spot.)

 

We can probably ask him if he has any developer documentation for the 74 - I think he likely still has access.  I'll see what he knows.

[+acadiel]

I talked to Stephen.  Yes, there was a TI-74 SDK.  No, you cannot get it any longer, and it also required a NDA because it is TI Proprietary information.  So, it’s a catch 22. To open source it would require that Stephen interrupt his other work to review it and be made available to answer questions about the code - which also, he doesn’t have time to do.

If there are particular questions about things like the cartridge pinout that we can get him to answer that don’t violate his work agreement, we can ask.  

[KlausO]

The simplest solution to the problem is definitely a 32kB RAM module that you somehow procure or build yourself. All ROMs as well as the PASCAL ROM have 32k. I converted two of my 8k RAM cartridges to 32 KRAM cartridges. This website shows what an 8K RAM cartridge looks like from the inside:

TEXAS TI-74 BASICALC & 8K RAM Cartridge teardown
https://www.hpmuseum.org/forum/thread-7146.html?highlight=TI-74

(The Post: # 5 shows a schematic diagram)

A 32k static RAM IC of the TYPE HM62256ALF-70 has 28 pins and thus exactly as many as the 8K RAM IC HM6264. Only PIN 1 and 26 differ. Pin 1 is not used at all in the 8k cartridge and must be connected to A14. A14 can be found on the underside at the second contact from the right, where the blue cable is soldered on in the photo. 

Pin 26 is connected to 5V in the 8k cartridge and is therefore permanently high. This means that PIN26 of the HM62256 must not have any connection with this. I therefore carefully bent this pin up a little before soldering it in. The bent pin is then connected to A13 with a cable. A13 can be found on the top at the third contact from the right.

 

Summary
bottom side: second contact from the right to the first PIN from the right in the top row on the upper side.
upper side: third contact from the right to the third bent PIN from the right.

 

The 32k RAM Cartridge works without a battery as long as it is plugged into the TI-74 (or TI-95). When pulled out, however, it loses its content without a battery. I use one with and the other without a battery.

 

With the program RWRAM.B74 the contents of RAM and ROM cartridges can be saved and loaded back into RAM cartridges. To do this, the function IOX.SUB has to be loaded beforehand with LOAD.PGM. All three files are part of the TIIF2.zip archive on http://pengels.bplaced.net/index.php/tiif/

 

The TI-74S was used a lot by insurance agents along with the necessary software in cartridges. In order to be able to adapt this software, some of the first generation of FLASH chips were used. Peter and I worked out how these FLASH chips can be erased and rewritten with the TI-74. The prerequisite is that the required 12 V programming voltage can be connected. This works with all cartridges with a hole for the power supply, as shown in the last picture. I don't know whether these cartridges were also available in other countries or only in Germany. If someone has one and wants to try it out, I can explain how. It's not going to be fast nor is it easy but it works.