Meilhaus Electronic ME-1400, Electronic Manual

Page: 11 / 29

3.2 Digital-I/O Section
For the programmable input/output component (PIO) the standard
component 82C55 (fully compatible CMOS-version of the 8255A) is
used. This component has 3 x 8-bit-wide programmable I/O ports
and is TTL/CMOS compatible.
The 8-bit-wide digital-I/O ports can be configured independently as
input or output. After power-up all ports are configured as input.
Make sure the voltage levels of the I/Os keep within the TTL level-
limits (see specifications on page 21) and that a reference to PC
ground (GND) must be done. The maximum output current is I
Out
=
I
OL
= I
OH
= 2.5 mA.
For programming the digital-I/O section please read chapter 4.1
"Digital I/O" on page 17.
3.3 Counter (8254)
The counter component is the standard type 82C54. This flexible
device has 3 independent 16-bit-(down) counters. All counter
signals are available on the D-sub connector. After the GATE-signal
has been properly set (5V) the counter counts down on every falling
edge.
The counter clock can be sourced alternatively by the internal
oscillator (1 MHz/10 MHz), externally (10 MHz max.) or by
cascading. The internal oscillator can be set separately for each
counter component from 1 MHz (default) to 10 MHz. The settings
are done by software. After power-up or after reset all counters
are configured for an external clock source. See also chapter
programming and the block diagrams from page 10 up.