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Alarm Condition

Software has no write access to the Alarm bit in register C, it can only read it. Alarm conditions are detected and reported by the Drive circuitry only.

An alarm condition does not prevent further Drive functionality in any way. Its only effect is to illuminate the Alarm Lamp to alert the Operator.

The following conditions cause the Alarm Lamp to illuminate.

  * Software writes an illegal Mode to register C.
  * Read or Write operation aborted because tape reaches its end (EOT).
  * Software attempts to make a WRITE operation while the Write Protect switch is in active position.

The only way to turn the lamp off again is by pressing the Clear Alarm button.

LC-81 Homebrew Minicomputer -- this software is based on Help Books running at melissa