Vector 4 - Page 110

VECTOR 4
TECHNICAL INFORMATION
5.3 HOW THE PARALLEL PORTS WORK
Summary: The SBC has one 8255 chip which is configured to provide
three data ports and one control port. This section will briefly
describe the operation of the 8255 in the VECTOR 4 environment.
The 8255 is addressed using the port decoding scheme described in Section 5.1.
This involves the decoding of the address lines through the use of Port Decoder 1.
This decoding process results in the generation of P189| and P1AB| whiech are used
to chip select the 82553.
The port assignments for the 8255 are:
8259 Port SBC Port - Function
A 08H Output to J4 and J3 connectors
B 09H QOutput to J4 and J3 connectors
C 0AH Input from J4 and J3 connectors
Control 0BH Sets PPI (8255) to 2 control and 1 ciata port
configuration (See Exhibit II-22). This is
accomplished by sending 89H to this port.
The J3 connector is a telephone-type, 50-pin connector. It can be used to attach
printers which require "Qume Type" parallel protocol. This protocol is described in
The J2 connector is also a telephone-type connector. It has 36 pins and uses
"Centronics Type" parallel protocol. This protocol is deseribed in Exhibit II-24.
See the VECTOR 4 PROGRAMMERS GUIDE for a complete description of the
printer drivers supplied with Vector Computer Systems.
09-01-82 7200-0001 II 5-19