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 parallel outputs for 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 module rack. 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
switches or other TTL type devices to the digital I/O
lines. The MPS-XX series boards accept G4 series
modules.
A CMA-26-24 connects J3 on the RPC-320 to the MPS-
XX board. Cable length 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 outputs 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
external opto module rack position 0. If the module 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 example 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 devices. Lines 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-XX series opto racks also provide 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
closure to ground at a line is read as a 0 using the LINE
# function at J1. 10K resistors are always pulled up at
lines L0 to L7.
When W7 configures the input resistors as pull downs,
one end of the switch must 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 programm ing example
The following example reads a switch at port A, bit 3
(J3-25) (program line 200), reads L1 at P6 (program line
210) and turns on opto module at channel 5 (program
line 220). A LED 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.
