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
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.
