Cassette Interface now works!!

What have you built or do you want to design to go with your replica 1

Speaking of noise...

Postby Aaron Teeling » Nov Wed 21, 2007 9:26 am

Vince,

To just throw it out there, is it possible that the noise from the Replica-1 operating is causing the problem?. When I turn on my computer, the radio on my workbench goes completely silent across the spectrum. I get a lot of video interference too so I started experimenting with aluminum foil shielding cut down the RF.

Seems with the inconsistent nature of your failures, it may be environment and not design.

On one ship I was on, every time the General Alarm was activated for more than 3 seconds, we would get a Hydrogen Sulfide detected alarm at the console. We determined that the cable for the alarm ran too close to the comms cabling, causing the computer to see a false positive from the detector interface. Something would wouldn't expect from shielded cabling running three feet apart.

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Postby vbriel » Nov Wed 21, 2007 3:01 pm

Aaron,

You have a good point and it is possible. I need to create a shielding device and test it more after this weekend.

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Postby logjam » Nov Wed 28, 2007 3:06 pm

Do you have a reproduction Apple 1 cassette interface to test?

I would think its a clock speed issue, but I would also think that if it were that it would still be able to read back its on recording...
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Postby mfortuna » Dec Wed 12, 2007 4:02 pm

I don't know the details of the Apple I cassette interface but I know how the TRS-80 works (or is supposed to work) at a high level. I hate analog too. On the TRS-80 the data bits are interleaved between clock bits. On reads the computer detects a clock bit at regular intervals. At half intervals it samples data. Absence of a pulse is a 0, presence of a pulse is a one.

I don't know if the firmware for either machine uses a window to sample the clock and data. Once it finds the clock, future clocks should arrive a known time +/- some amount that is based on tape speed error. Future data bits will arrive much the same way.

What it sounds like you are seeing is an extra clock and are sampling the same 0 bit twice. This will cause all future bytes to be shifted right and will turn 0x20s into 0x10s, etc.

It could be the firmware slipped a bit while writing. The best way to figure that out would be to write a tape on a known good apple I and then read it on the replica I or do the reverse.

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Postby vbriel » Dec Thu 13, 2007 11:52 pm

I haven't had a minute to work on anything, but last time I hooked up a board, it started dropping the high bit after about 256-512 bytes. I'll look into this but lately the family and job has taken up all my free time. I haven't even had time to play with my replica in a while!

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