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APPENDIX F
THE
PARALLEL INTERFACE
This printer has a parallel interface to communicate with the
computer. The operating specifications of the parallel interface
are as follows:
Data transfer rate:
1,000 to 6,000 characters per second
Synchronization:
Via externally supplied STROBE pulses
Handshaking:
ACK and BUSY signals
Logic level:
Compatible with TTL level
The parallel interface connects to the computer by a 36 pin
connector on the back of the printer. This connector mates with
an Amphenol 57-30360 connector. The functions of the various
pins are summarized in Table F-1.
b Functions of the Connector Signals
Communications between the computer and the printer use
many of the pins of the connector. To understand how the
system of communications works, let’s look at the functions of
the various signals carried by the pins of the interface connec-
tor.
Pin 1 carries the STROBE pulse signal from the computer to
the printer. This signal is normally held high by the computer.
When the computer has data ready for the printer it sets this
signal to a low value for at least 0.5 microseconds. When the
printer sees this pulse on the strobe pin, it reads the data that
the computer supplies on pins 2 through 9. Each of these lines
carries one bit of information. A logical “l” is represented by a
high signal level, and a logical “O”is represented by a low signal
level. The computer must maintain these signals for a period
beginning at least 0.5 microseconds before the strobe pulse
starts and continuing for at least 0.5 microseconds after the
strobe pulse ends.