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Appendix
Code
The hexadecimal numbers corresponding to the XON/XOFF codes are shown below.
XON code: 11H
XOFF code: 13H
IEEE 1284 Parallel Interface
Modes
The IEEE 1284 parallel interface supports the following two modes.
Compatibility Mode
Compatibility mode allows data transmission from host to printer only: Centronics-compatible.
Specification
Reverse Mode
The transfer of status data from the printer to the host proceeds in the nibble or byte mode.
This mode allows data transfer from an asynchronous printer under the control of the host. Data transfers in
the nibble mode are made via the existing control lines in units of four bits (a nibble). In the byte mode, data
transfer proceeds by making the 8-bit data lines bidirectional. Both modes fail to proceed concurrently in the
compatibility mode, thereby causing half-duplex transmission.
CAUTION
When the printer goes from offline to online and the receive buffer is full, XON is not
transmitted.
When the printer goes from online to offline and the receive buffer is full, XOFF is not
transmitted.
When DIP switch 1-3 is off, XON is not transmitted as long as the printer is offline, even if a
receive buffer full state has been cleared.
Mode Communication direction Other information
Compatibility mode Host Printer communication Centronics-compliant
Reverse mode Printer Host communication Assumes a data transfer from an asynchronous
printer
Data transmission 8-bit parallel
Synchronization Externally supplied STROBE
signals
Handshaking ACK
and BUSY signals
Signal levels TTL-compatible connector
Connector ADS-B36BLFDR176 (HONDA) or equivalent product
Reverse communication Nibble or byte mode
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