Motorola Symbol PL4507 Integration Manual page 204

9 - 36 Symbol PL4507 Decoder Integration Guide
Overfilling Transmission Buffer
The Code 39 buffer holds 200 characters. If the symbol just read results in an overflow of the transmission buffer:
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The decoder indicates that the symbol was rejected by issuing three long, high beeps.
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No transmission occurs. The data in the buffer is not affected.
Attempt to Transmit an Empty Buffer
If the symbol just read was the Transmit Buffer symbol and the Code 39 buffer is empty:
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A short lo/hi/lo beep signals that the buffer is empty.
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No transmission occurs.
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The buffer remains empty.