Texas Instruments 99/4A - Page 17

HOME COMPUTER CASSETTE INTERFACE
1. Operates with byte/manchester encoding format.
2. Utilizes redundancy to gain increased reliability.
3. Uses wave shaping on input and output to increase reliability.
4. Has two motor control circuits which allow computer to control
dec ks -
5. Has capability of reading from one deck and writinq to another,
under computer control .
6. The interface is software intensive and relies on 9901 internal
timer for it's timing.
PROBLEM AREA OF CASSETTE INTERFACE
1. Reliable recovery of data is dependant on recorder used during
save.
2. Reliability is directly proportional to frequency response of
cassette deck.
3. Reliability can be observed by looking for the "eye" or ’ ’ jitter ”
phenomenon with an oscilloscope.
A. Present reliability is dependant on amount of jitter. If
jitter is less than 60 ms cassette should work.
4. Cassette is also adversely affected by speed changes.
A. Motor control circuit can under special circumstances cause
this.
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