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TI-74 and cassette capabilities


acadiel

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I started this thread over at VCFed - it might get a little more traction here. We were talking about the TI-74 cassette cable. The 74 (and CC-40+) have a cassette capability in their ROM. And, they appear to do it entirely over the data line of the Hexbus Interface. Here's what I posted on vcfed below. Of most interest is the YouTube video and Stack Exchange discussion. The pictures on Datamath don't show anything remarkable inside the interface itself. The TI-74 ROM has been dumped. Ksarul has the CC-40+ ROM as well, which also has cassette capabilities, and we can easily dump that, too.

 

CC-40+ cassette demo video stars here: https://youtu.be/e5YLiarJjnk?t=4m45s

Tape audio - higher volume: https://www.dropbox.com/s/9zl5bzmdn7e4yd0/cc-40plus_highervolume.wav?dl=0

Tape audio - lower volume: https://www.dropbox.com/s/tgx1dqsd01s691p/cc-40plus_lowervolume.wav?dl=0

 

* quote *

 

I'm wondering if we could easily make one.

 

Jim Brain has been helping us out with CC-40 peripherals lately. The 74 has the cassette stuff mostly built in.

 

Some folks on Stack exchange got a rudimentary interface going: https://electronics.stackexchange.co...lculator-ti-74

Here's what the innards of the cassette interface looks like: http://www.datamath.org/Graphing/JPEG_CI-7.htm#PCB

YouTube video of what the cassette signal sounded like: https://www.youtube.com/watch?v=q_Tu...ature=youtu.be

 

Note that the interface is just a 74HC367 (3 state hex line buffer/line driver), a CA358E (Op Amp), and a bunch of caps, resistors, and transistors.

 

"Paolo" on the Stack Exchange discussion was on the right track for a home-brew adapter: http://www.datamath.org/Graphing/JPEG_CI-7.htm#PCB

 

------ clip ------

I realized such an Interface severals years ago. The "Data Output" pin is pin #6 --> D3. The "Data Input" pin is pin#3 --> D0.

 

Recording:

 

you are on the right way: just use a voltage divider (e.g. 2 resisitors) to match the voltage requirements your recorder. A 100nF capacitor between voltage divider and mic-input could help.

 

Playback:

 

You have to clean and amplify the recorded signal, it must be a square wave, with low state = "GND" and high state = "VCC".

 

I used a common LM358N as non inverting Schmitt-Trigger to obtain a clean wave. It'easy, you need only 4 resistors. I played wit several resistor values, I obtained the best results with a 0,3V treshold.

 

You can supply the LM358N from Pin#1. Ok, it drains power, but not noticeably icon_wink.gif

 

I used the same interface with a Sharp PC-1260: VCC: pin#2, GND; pin#3, data in: pin#6, data out: pin#7

 

Have fun! icon_smile.gif

 

Paolo

------ clip ------

Also, here is the orientation of my interface and cable.

 

f4c47e7ba3609294fa1b60bddbba0a88.jpg

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Thanks for this information - interesting! I recently acquired a TI-74, so I am interested in information about it. I just have a the computer, and no peripherals or ROM/RAM modules. I haven't had much time to spend with it, but it appears that assembly programming on the stock machine is not a possibility.

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Thanks for this information - interesting! I recently acquired a TI-74, so I am interested in information about it. I just have a the computer, and no peripherals or ROM/RAM modules. I haven't had much time to spend with it, but it appears that assembly programming on the stock machine is not a possibility.

 

I you are willing to hand assemble the instructions and poke them into memory from Basic, it should be feasible :)

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I you are willing to hand assemble the instructions and poke them into memory from Basic, it should be feasible :)

 

That's the problem. The 74 and 95 didn't let anyone directly poke or peek anything from stock BASIC, nor did the systems have a debugger. You had to actually get the PC-IF and upload assembly from a PC. That's how the ROM got dumped (bank switched ROM) by, I believe, JGardner on vcfed. He sent assembly to the unit that did bank switching and fetched the 8K bank switched segments of the 32K ROM, as well as the CPU ROM segment.

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Did not remember the T74 had no POKE facility... I have a PCIF with the PC drivers and it works just fine on DOS computers. If you are up to the task of reverse engineering it, I can see if I can open it up and take some pictures next week when I come off service.

 

That sounds great for the PC-IF! Higher resolution pics from multiple angles, and maybe a pinout from the connector to the main PCB.

 

Also, on the CI-7 front - The CI-7 cassette interface looks really simple for me to breadboard if I can get higher resolution pics of it too.

 

BTW, the 4K Processor ROM on the 74 is what houses the cassette routines. I found the cassette messages there. TI's nomenclature was that the 7040 type series that the 74 had meant 4K of on processor ROM. The CC-40 had a 7020 type, or 2K of on processor ROM. I don't know what the CC-40+ had, because if I recall correctly, it had an experimental designation on it's CPU.

 

Edit: TMS7000 family data manual for those wanting the opcodes for disassembling.

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Can you access the printer port directly through Windows 7 and up? As I recall, the problem with using an XM1541 cable is that past Windows XP the printer port is not directly accessible.

 

What about a USB-based rendition?

From the docs (tiif.txt): "Since Windows XP and newer doesn't allow direct access to the IO-port of the LPT-card, a system kernel driver is required. I decided to use TVicPort (http://entechtaiwan.com/dev/port/index.shtm) which is free for non commercial use. This combination was successfully tested on a Windows 10 32 Bit PC with an onboard LPT-port and a Windows 10 64 Bit PC with a PCIe LPT-port."

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This actually looks pretty simple.

:)

 

 

 

Yes it does. As I am working on the ET-PEB in the coming weeks I was thinking it could also be configured as TI-74 PC interface over USB serial port.

 

I don't have other manuals than the technical manual for the TI-74. How would one communicate with a PC using the PC interface? Is it for saving and loading "only"? What would be the commands?

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From the docs (tiif.txt): "Since Windows XP and newer doesn't allow direct access to the IO-port of the LPT-card, a system kernel driver is required. I decided to use TVicPort (http://entechtaiwan.com/dev/port/index.shtm) which is free for non commercial use. This combination was successfully tested on a Windows 10 32 Bit PC with an onboard LPT-port and a Windows 10 64 Bit PC with a PCIe LPT-port."

 

Nice. I only looked at the schematics. Wish that could have been done with the XM1541. Seemed a lot more reliable (or at least less picky) than the USB driver for the XU.

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It looks like a simple bit banging type interface. We can probably adapt it to USB, but it's going to be getting the timing right. Brain already has most of the timing and protocol figured out for his CC-40 cassette interface. We can probably use some of the site Jens-Eike posted above for the rest of the protocol/interface.

 

Really, I think we can probably build the "PC" part of the interface into USB on Brain's CC-40 SD card solution so that it works with the PCIF2 suite above. Jim, what are your thoughts on this?

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  • 4 weeks later...

202506447c99f94c7c2598e116952491.jpg

Got ahold of a TI-74S with some German software; Hamburg-Mannheimer, installed. Heard some rumors that CALL ADDMEM would add 16K with a ram cart instead of 8K for the plain 74. Anyone know any other differences?

 

Edit: Another cool link of a teardown of the 8K RAM cart:

 

http://www.hpmuseum.org/forum/archive/index.php?thread-7146.html

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Hamburg-Mannheimer was a former insurance company. It was bought by the ERGO insurance group.

 

It says

 

left

"Calculation for

UV = accident analysis

VHO = Alimentation analysis HO

 

Tariffs

..."

 

right

"Function keys

Enter or

Arrow down - proceed in program

Arrow up - step back in program

Arrow right/left - move in entry field

Mode - calculation (after change)

CLR - clear entry field"

 

The box lists some rebates for insurance sums, and a hint for the insurance agent to suggest a higher sum to the client for a higher rebate.

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