Appendix
D
Publication 17706.5.20 - June 1997
Writing a Parallel
Communication Driver
The KFC15/KFCD15 supports both full-duplex and half-duplex DF1
protocol over the RS-232C link. For details of the protocol format,
refer to the document Allen-Bradley Data Highway/Data Highway
Plus/DH-485 Communication Protocol and Command Set Reference
Manual (1770-6.5.16).
DF1 Parallel Communication
To communicate over the parallel port between a host computer and
the KFC15/KFCD15 use the link layer protocol of half-duplex DF1.
In this setup, the computer is the host device and the
KFC15/KFCD15 is the peripheral.
If the host supports bidirectional data on the parallel port you can use
the Byte Transfer Mode. If the host supports output data only on the
parallel port use Nibble Transfer Mode.
In Byte Transfer Mode, the host transmits and receives data one byte
(eight bits) at a time. In Nibble Transfer Mode, the host transmits
data one byte at a time, but receives data from the KFC15/KFCD15
one nibble (four bits) at a time.
The physical interface consists of eight data lines and nine
handshaking lines. Four of the handshaking lines are controlled by
the host and five by the KFC15/KFCD15. The table below shows
how the lines of the parallel port are used for both Byte and Nibble
modes.