Clone Cassette Adapter With 88-2SIOJP?

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

Clone Cassette Adapter With 88-2SIOJP?

Postby toml_12953 » February 14th, 2019, 3:49 pm

Does anyone know if the Clone Cassette adapter can work with Martin Eberhard's 88-2SIOJP serial port board? I know you can set either of the two ports on the board as TTL levels
but I don't know if that would work with the Cassette adapter. Also in a system with +8v and +/-16v, where would I get the 3.3v needed for the adapter?

If you know a way I can get it to work, PLEASE let me know with precise instructions! I'm not a hardware person (just look at my other posts to verify that!)
so I'd need "Connect the RX line to pin 4 of the serial port board, then connect the TX line to..." type of instructions.

Thanks for any help you could give!
toml_12953
 
Posts: 161
Joined: June 7th, 2013, 12:54 pm

Re: Clone Cassette Adapter With 88-2SIOJP?

Postby AltairClone » February 14th, 2019, 11:00 pm

The Altair Clone cassette interface can be run at 5v instead of 3.3v without any problem. If you had an original 88-SIO B board (the TTL level serial board which was piggy-backed with the original ACR modem board), it would work fine with the Altair Clone cassette board and you’d have a working S100 cassette interface.

However, neither the original 88-2SIO or Martin’s 2SIOJP can work as the serial interface for either the original ACR modem or the Altair Clone cassette board. First, the control/status register bit positions and polarity are different than the SIO used with the ACR, and second, the TTL interfaces on the 2SIO (and 2SIOJP) invert the data instead of simply buffering it straight through.

Mike
AltairClone
Site Admin
 
Posts: 364
Joined: April 5th, 2013, 10:55 am

Re: Clone Cassette Adapter With 88-2SIOJP?

Postby TomXP411 » February 15th, 2019, 1:50 am

Mike,

Can you use something like a Max232 to convert the RS-232 signals back to TTL? If someone hooked a Max232 up to the cassette board, would that work, or would the signal still be upside-down?
TomXP411
 
Posts: 29
Joined: March 8th, 2018, 4:13 pm

Re: Clone Cassette Adapter With 88-2SIOJP?

Postby AltairClone » February 15th, 2019, 2:12 pm

The PIC processor on the Clone cassette interface board sits in the middle and simply bit-bangs serial I/O back and forth, so the simplest solution to the polarity issue is a quick update to the firmware on the PIC.

However, this still leaves the problem that none of the existing cassette software will work since the UART on the 2SIO is different than that used on the original SIO-B used with MITS 88-ACR.

Mike
work a
AltairClone
Site Admin
 
Posts: 364
Joined: April 5th, 2013, 10:55 am

Re: Clone Cassette Adapter With 88-2SIOJP?

Postby TomXP411 » February 15th, 2019, 2:15 pm

Okay, so the problem isn't a physical one - you're saying that the registers on the chips are different, so the software won't know how to deal with it.

That makes sense, and I can see why that would cause an issue.
TomXP411
 
Posts: 29
Joined: March 8th, 2018, 4:13 pm


Return to Altair 8800c

Who is online

Users browsing this forum: No registered users and 0 guests

cron