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B–3
Host I/O Interfaces
Centronics Parallel Interface Signals
The Centronics interface signals are defined below.
PAPER EMPTY – A high true level from the printer to indicate the printer is in
a fault condition.
SELECT – A high true level from the printer to indicate the printer is ready for
data transfer and the ON LINE switch has been activated.
BUSY – A high true level from the printer to indicate the printer cannot receive
data.
ACKNOWLEDGE – A low true pulse from the printer indicating the character
or function code has been received and the printer is ready for the next data
transfer.
DATA STROBE – A low true, 100 ns minimum pulse from the host to clock
data into the printer.
DATA LINES – Eight standard or inverted levels from the host that define the
data, which may consist of a character or function code. Sensing Data Line 8 is
controlled by printer configuration.
PAPER INST – Optional VFU control signal from the host with the same timing
and polarity as the data lines. PI line sensing is controlled by printer
configuration.
NOTE: The PAPER INST line must be disabled (configuration option
selected from the front panel) if the host does not drive or control it.
If the line is not controlled by the host and sensing is enabled, rapid
paper slewing will occur.