– 21 –
Sends <ENQ>
Receives status byte.
Sends <STX>
Is the data buffer
empty?
Is an odd parity
check?
Acquires the exclusive OR of the content
of the text byte and the data to sent, then
it is used as the content of the test byte.
Transmits the data to
the printer.
Is this the last data in
a block?
Starts the
STX-ETX mode.
The test byte is set at (0)H.
Sends an <ENQ>
Receives status signal.
Receives a check byte.
Sends <ETX>
Sends <CAN>
Ends the
STX-ETX mode.
RET
Is there a data block in
the STX-ETX mode?
YES
NO
(Printing)
NO
YES
YES
NO
YES
NO
YES
NO
Horizontal
parity check
Check byte =
test byte?
Is the status an
error?
YES
(FF) H is set for the text
byte.
NO
Check byte:
Horizotal parity of the printer.
Test byte:
Horrizontal parity of the host
computer.
STX-ETX mode flow diagram for host computer
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