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Read

The READ operation is initiated by Software writing Mode READ to register C. An interrupt is asserted to confirm that mode has changed.

The Drive makes preparations to start reading the tape starting at the current tape position. If it happens to be in a GAP (as it is supposed to), reading starts at the first bit of the block following the GAP. If it is in a data zone instead, the Drive skips to the next GAP, then start reading the next block.

Once an entire byte has been decoded, it is copied to register D and an interrupt is asserted to notify that a byte is waiting for reading. The Software must act quickly to read that byte from D. This process continues, byte after byte, until a GAP is reached in which case the Drive automatically changes to Mode STOP and another interrupt is asserted to notify that.

Software can also abort the READ operation by writing Mode STOP to register C, which is not advisable in normal circumstances because then the tape would stop in data area instead of on a GAP. Software is expected to read an entire block into a buffer. Once the block has been read and the tape has stopped, Software is plenty of time to process that block for their own purposes.