Epson TM-T90 Specification page 45

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2.1.2.7 Reception of status from the printer through the bidirectional parallel interface
In the bidirectional parallel interface specifications, the printer status transmission is available by using
the both-way communication facility in the Nibble/Byte Modes in accordance with the IEEE 1284.
This case is different from in the RS-232 serial interface specifications where the real-time interruptions
from the printer to the host are disabled, and thus precautions must be taken:
1) Allowable capacity of the printer internal buffer is 99 bytes (except ASB status). Status signals
exceeding this capacity will be discarded. To prevent possible loss of status, the host shall be
ready for data reception (Reverse Mode).
2) When ASB is used, the host is preferably in the wait state for data reception (Reverse Idle Mode).
When this state is not available, the host shall enter the Reverse Mode to constantly monitor the
presence of data.
3) When ASB is used, preference shall be given to the ASB status for transmission over the other
status signals.
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