Specifications

Parallel I/O
FUNCTIONAL DESCRIPTION
A functional diagram of each of the 24 I/O signals is illustrated in
Figure 12-1. The diagram includes an Output Latch, an Output Buffer,
and an Input Buffer. These functional blocks are described below.
Output
Latch
The Output Latch stores the data present on the internal data bus
during a write operation to the parallel port. The data is latched until
altered by another parallel port write or until power is turned off.
While the Output Latch is not initialized after power-up, the state of
the parallel I/O signal at connector J1 is a TTL high because the
Output Buffer is disabled and the passive termination is in effect.
82050 Serial Port OUT2 Bit
Internal Data Bus
Output
Data Latch
Passive Termination
Output
Buffer
Input
Buffer
Connector J1
Figure 12–1. Parallel Port Functional Diagram.
12-3