Appendix
97
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.
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 nStrobe signals
Handshaking nAck and BUSY signals
Signal levels TTL-compatible connector
Connector ADS-B36BLFDR176 (HONDA) or equivalent product
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