Introduction
Centronics Printer/General Purpose I/O Port
A Centronics printer interface is included on the ZT 8809A. It may
drive a Centronics-compatible printer directly. The printer interface
can also be used for general purpose I/O. It consists of eight I/O lines
for data, four open collector I/O lines for control, and five input lines
for status. The open collector lines have internal 2.5 k
Ω
pullups to
Vcc.
One of the status lines, ACK, activates the interrupt request LPT1
from the printer interface to the interrupt controller. An enable bit for
this interrupt is within the printer interface chip, the VL 16C452.
(This chip also contains the two 16C450 equivalent serial ports.) All
lines have corresponding register bits within the 16C452.
Optional Numeric Data Coprocessor (8087)
An Intel 8087 or equivalent Numeric Data Coprocessor is available
for the ZT 8809A. It adds performance by contributing arithmetic,
trigonometric, exponential,
and logarithmic instructions to the
standard 8088/8086 instruction set.
The 8087 may be mounted on the ZT 8809A with the aid of Ziatech’s
zSBC 337 module. This module mounts onto the microprocessor
socket and accepts both the microprocessor and 8087.
This
configuration requires two slots in a standard STD bus card cage
unless mounted in the end slot.
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