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TI-74 and cassette capabilities


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#1 acadiel ONLINE  

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Posted Wed Jan 10, 2018 3:31 PM

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....volume.wav?dl=0
Tape audio - lower volume: https://www.dropbox....volume.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.....lculator-ti-74
Here's what the innards of the cassette interface looks like: http://www.datamath....EG_CI-7.htm#PCB
YouTube video of what the cassette signal sounded like: https://www.youtube.....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....EG_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

#2 acadiel ONLINE  

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Posted Wed Jan 10, 2018 4:33 PM

YouTube video that confirms that D3 and ground is the cassette output:
 



#3 Opry99er OFFLINE  

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Posted Wed Jan 10, 2018 6:42 PM

Cool! Can we load back to the machine via a cassette as well? (I do not know much about this computer)

#4 acadiel ONLINE  

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Posted Wed Jan 10, 2018 8:10 PM

Cool! Can we load back to the machine via a cassette as well? (I do not know much about this computer)

If we got the levels correct, yes.

Sent from my Moto Z (2) using Tapatalk

#5 speccery OFFLINE  

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Posted Thu Jan 11, 2018 8:11 AM

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.



#6 Vorticon OFFLINE  

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Posted Thu Jan 11, 2018 9:18 AM

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 :)



#7 acadiel ONLINE  

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Posted Thu Jan 11, 2018 10:41 AM

There was a PC interface that people used to send assembly programs to the unit.  I don't have a picture nor a schematic for this.  If anyone has any information on it, maybe we can replicate it.

 

ftp://ftp.whtech.com/hexbus_cc40_ti74/PC%20Interface%20(PCIF)%20manual.pdf



#8 acadiel ONLINE  

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Posted Thu Jan 11, 2018 2:08 PM

 

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.



#9 Vorticon OFFLINE  

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Posted Thu Jan 11, 2018 3:36 PM

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.



#10 acadiel ONLINE  

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Posted Thu Jan 11, 2018 4:57 PM

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.  



#11 speccery OFFLINE  

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Posted Sat Jan 13, 2018 4:04 AM

Acadiel mentioned that the TI-74 ROM has been dumped, including the paged portion. Is that dump somewhere available?



#12 speccery OFFLINE  

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Posted Sat Jan 13, 2018 4:05 AM

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

 

Thanks for the link to the TMS7000 disassembler. this is probably the first program in the "go" language I have looked at..



#13 apersson850 OFFLINE  

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Posted Sun Jan 14, 2018 8:08 AM

Hm, I actually have the original cassette interface for the TI-74 BASICALC somewhere. But I'm not 100% sure where it is right now.



#14 jens-eike OFFLINE  

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Posted Sun Jan 14, 2018 8:54 AM

In comp.sys.ti was a post about a new version of the PC-IF:

 

https://groups.googl....ti/WT3qdYD1tZE

 

the link to

 

acg-bonn.dyndns.org/~en/downloads/files/tiif.zip

 

still works, the file contains schematics and software from DOS to WIN32



#15 jens-eike OFFLINE  

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Posted Sun Jan 14, 2018 8:55 AM

just found a current version:

 

https://groups.googl....ti/_xbwmWs5gXY

 

http://pengels.bplac.../index.php/tiif



#16 acadiel ONLINE  

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Posted Sun Jan 14, 2018 12:23 PM

Acadiel mentioned that the TI-74 ROM has been dumped, including the paged portion. Is that dump somewhere available?

 

Here you go :)

Attached Files

  • Attached File  ti74.zip   30.11KB   5 downloads


#17 acadiel ONLINE  

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Posted Sun Jan 14, 2018 12:28 PM

 

 

This actually looks pretty simple.

:)

 

 

Attached Files



#18 OLD CS1 OFFLINE  

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Posted Sun Jan 14, 2018 12:46 PM

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?



#19 jens-eike OFFLINE  

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Posted Sun Jan 14, 2018 1:53 PM

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....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."



#20 speccery OFFLINE  

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Posted Sun Jan 14, 2018 2:03 PM

 

Here you go :)

 

 

Thanks a lot!



#21 speccery OFFLINE  

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Posted Sun Jan 14, 2018 2:05 PM

 

 

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?



#22 OLD CS1 OFFLINE  

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Posted Sun Jan 14, 2018 2:39 PM

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....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.



#23 acadiel ONLINE  

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Posted Mon Jan 15, 2018 9:02 AM

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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