Replacement for Altair Cassette Interface

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Replacement for Altair Cassette Interface

Postby AltairClone » October 31st, 2023, 8:41 am

Since the Altair Cassette Interface is difficult to find - and expensive when you do - I've recently demonstrated a way to make a drop-in replacement using more readily available and less expensive hardware. See https://www.youtube.com/watch?v=7OvUOx5KInc

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Re: Replacement for Altair Cassette Interface

Postby Wayne Parham » November 1st, 2023, 9:41 am

Great idea to use the modem you manufacture with an SIO port rather than trying to find an old original modem board. I like that you can use that board both in clones and in 8800c systems. Now that I think about it, you could even use it on an original 8800. I'm so glad you make those boards!
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Re: Replacement for Altair Cassette Interface

Postby toml_12953 » November 1st, 2023, 6:42 pm

Wayne Parham wrote:Great idea to use the modem you manufacture with an SIO port rather than trying to find an old original modem board. I like that you can use that board both in clones and in 8800c systems. Now that I think about it, you could even use it on an original 8800. I'm so glad you make those boards!


Now I wish he'd make the board the interface connects to! I can't find any of the boards he mentions in the instructions.
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Re: Replacement for Altair Cassette Interface

Postby toml_12953 » November 22nd, 2023, 7:14 am

toml_12953 wrote:
Wayne Parham wrote:Great idea to use the modem you manufacture with an SIO port rather than trying to find an old original modem board. I like that you can use that board both in clones and in 8800c systems. Now that I think about it, you could even use it on an original 8800. I'm so glad you make those boards!


Now I wish he'd make the board the interface connects to! I can't find any of the boards he mentions in the instructions.


Of course, just a few days after I posted the above, I saw an SSM IO-4 board up for auction! I have a bid in on it. When I look at the video for using it to connect to the cassette interface, though, I can't make out which to use for U16 and U18 - SN74367 or SN74368. Should they both be the same? I figure I should use the SN74368 but want to make sure. Also, what are the connections from the serial port socket to the cassette board? I'm looking at the SSM manual and it lists serial connections +RL, -RL, --RL, +TL, -TL, --TL. I figure R is receive and T is transmit but what's with the +, - and -- ? If I want to go from the SSM directly to the cassette interface rather than run a DB-25 cable out the back, what should I connect to what?
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Re: Replacement for Altair Cassette Interface

Postby AltairClone » November 22nd, 2023, 8:47 am

You can find the schematic for the IO4 board in the version of the manual linked below:

https://deramp.com/downloads/mfe_archiv ... Manual.pdf
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Re: Replacement for Altair Cassette Interface

Postby toml_12953 » November 26th, 2023, 6:58 pm

The 8800b Turnkey board has a serial port on it. Does anyone know if it's compatible with the original SIO or the later 2SIO?
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Re: Replacement for Altair Cassette Interface

Postby AltairClone » November 26th, 2023, 8:41 pm

It’s a 2SIO port using the 6850 ACIA.

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Re: Replacement for Altair Cassette Interface

Postby toml_12953 » November 29th, 2023, 3:51 pm

I just bought an Altair 88-2 SIOB on eBay. While I'm waiting for it to arrive, I'd like to figure out the interconnections to the Clone cassette interface.
If the photo in the ad is correct, right now the board I'm getting is set to
octal address 006, 110 baud, 2 stop bits, no parity, 8 bits/character.
I believe the address is OK.
I can change the baud rate to 300 with no problem.
Do I need to change the stop bits to 1?
8 bits/character should be OK, right?

About the connection to the Clone interface:
Since the SIOB is a TTL interface, I don't need to use the external DB-25 patch cable. When I use the Clone's interface as a serial port, it's 300 baud, correct?
For connection to the Clone board, I need a jumper between pins 2 & 4 of J2.

Are these connections correct?
SIOB STSO (Pin 10) to pin 4 on J1
SIOB SRSI (Pin 5) to pin 2 on J1
SIOB GND (Pin 4) to pin 5 on J1
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Re: Replacement for Altair Cassette Interface

Postby AltairClone » November 29th, 2023, 6:16 pm

I believe the address is OK. YES
I can change the baud rate to 300 with no problem. YES, DO THIS
Do I need to change the stop bits to 1? IT’S FASTER AND THAT’S HOW MITS CONFIGURED IT
8 bits/character should be OK, right? YES

About the connection to the Clone interface:
Since the SIOB is a TTL interface, I don't need to use the external DB-25 patch cable. When I use the Clone's interface as a serial port, it's 300 baud, correct? YES
For connection to the Clone board, I need a jumper between pins 2 & 4 of J2. TO USE A TTL INTERFACE TO THE CLONE CASSETTE BOARD, YES

Are these connections correct? YES. YOU’LL ALSO NEED TO CONNECT +5v FROM THE SIOB TO J1 PIN 1.
SIOB STSO (Pin 10) to pin 4 on J1
SIOB SRSI (Pin 5) to pin 2 on J1
SIOB GND (Pin 4) to pin 5 on J1
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Re: Replacement for Altair Cassette Interface

Postby tubarespect » January 7th, 2024, 3:36 pm

Would it be possible to use a SSM IO-2 board instead of the IO-4? Reading the IO-2 user manual, it appears to state that it is possible to configure the board as an Altair SIO Rev 1 compatible card.

There are reproduction boards without components installed currently for sale made by Glitch Works.

Here is a link to the manual I am referencing:
https://deramp.com/downloads/mfe_archive/010-S100%20Computers%20and%20Boards/01-Solid%20State%20Music/10-SSM%20S100%20Boards/SSM%20IO2/IO2_Parallel_IO_Board.pdf
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