DIGITAL AND OPTO PORTS
SECTION 6
Page 6-4 RPC -320
Figure 6-2 Inductive load protection
Protection diodes m ust be used with inductive loads.
Refer to figure 6-2
Do not pa rallel outputs f or higher drive. This could
result in damage since outputs will not share current
equally.
The outputs at U12 are open collector. An external
device must supply power.
Interfacing Digital I/O to an opto-module rack
I/O lines at J3 can interface to an MPS-8, 16, or 24
position opto m odule rac k. L ines not going to an opto
module connect to a screw terminal on the MPS-XX
series boards. This feature allows you to connect
s w it ch e s o r ot he r T T L t yp e de v ic e s t o t he d ig it al I/ O
lines. The MPS-XX series boards accept G4 series
modules.
A CM A-26-24 connects J3 on the RPC-320 to the MP S-
XX bo ard. Cable len gth should be less than 2 feet.
Excessive cable lengths cause a voltage drop and
consequently unreliable operation. Make sure + 5 V and
ground is connected to the M PS-XX racks.
Before a line is set, the 82C55 chip must be initialized.
This is done using the CONFIG LINE statement. Group
inputs and outpu ts together. Refer to Table 6-1 for opto
module position, port number , and connector pin out. If
opto channels 16-23 are used, U12 should be replaced by
a DIP shunt jumper.
The LINE and LINE # com mands are used to control
and access opto modules and lines. These commands are
both functions and statements, depending upon how they
are used.
100 LINE 100, 0
Statement
110 LINE #103, 0
Statement
120 A = LINE(100)
Function
130
A = LINE#(103)
Function
Program line 100 turns external opto module rack
position 0 off. Program line 110 sets J3, pin 3, to a
logical 0 level. Program line 120 returns the status of
externa l opto modu le rack po sition 0. If the modu le is
"off", a 1 is returned (assuming it is an output module).
Program line 130 returns the status of J3, pin 3 as a 0 or
1.
Example: To turn on opto module in slot position 8, the
following command is executed:
LINE 108, 1
A ' 1' turns on a module while a 0 turns it off. (In actual
fact, a 0 is written at the port. )
See
Digital I/ O program ming exam ple
later in this
chapter.
Interfacing to switches and other devices
Switches and other digital I/O devices may be connected
directly to P6 or J3. The STB-26 terminal board
provides a convenient way of interfacing switches or
other digital I/ O device s. L ines at J3 are connected to
the STB-26 with a CMA-26 cable. Digital devices are
then connected to the screw terminals on the STB-26.
The M PS-X X serie s opto rac ks also pro vide a way to
access digital I/O lines.
Switches may be connected directly to a line. When
jumper W7 configures the resistors as pull ups, a switch
c l os u re to g r ou n d a t a li ne is r ea d as a 0 u s in g th e L IN E
# function at J1. 10K resistors are always pulled up at
lines L0 to L7.
When W 7 configures the input re sistors as pull downs,
one end of the switch m ust be tied to + 5 volts. If this is
not possible or convenient, a 1K resistor can be tied
between an input and + 5 volts to force it high when a
switch is open.
Digital I/ O prog ramm ing exam ple
The follow ing exam ple read s a switch at po rt A, bit 3
(J3-25) (program line 200), r eads L1 at P6 (program line
210) and turns on opto module at channel 5 (program
line 220). A LE D is controlled through the high current
port at J3-10 (port B, bit 0) (program lines 230 and 240).
For testing, a 100 ohm resistor from J3-10 to + 5 volts
can be substituted.