12-1
RLC-4 V1.79 Copyright © 1998 Link Communications Inc. 9/18/98
Chapter 12: The I/O Interface
About the I/O System:
The RLC-4 provides 3 logical inputs, 4 logical outputs and 4 analog input lines. They are all
handled totally separately in software; each command applies to only one of the three types of lines.
Each type will be described below.
Please note that you can control how often the RLC-4 checks the input line and analog alarms by
using C020 to change the reset value of timer 16. The default is to check the alarms once per
second.
Logical Input Lines:
The logical input lines are used to detect whether a line is "high" or "low". High means that the
voltage read by that line is above approximately 2.5 volts. Low means that the voltage is below
about 1 volt. The range between 1 volt and 2.5 volts is indeterminate. If the line is not connected,
a 47K internal pullup resistor to 5 volts will make the line read high. This pullup allows you to
easily read whether a switch is open or closed. Simply connect the switch between the input line
and ground. If the switch is closed, the input will read low. If the switch is open, the pullup
resistor will make the input line read high. The input line can handle voltages up to +40 volts. Do
not apply negative voltage to an input line.
Input lines can be used in three ways.
• Command 090 can read an input line and tell you whether it is high or low.
• There is also a way to assign a custom CW message to each state of an input line, such as "door
open" and "door shut" (instead if high and low). To do this, program macros to send the CW
messages you want and use command 045 to assign which macros get executed when the input
lines change state. You can also cause those messages to be sent by executing command 091.
Logical Output Lines:
The logical outputs are "open collector" outputs. That means that they can connect the output line
to ground (turn it on) or disconnect it (turn it off). The output lines never output any voltage. The
way they are commonly used is to connect one lead of the coil of a relay (or whatever else you want
to control) to 12 volts and the other lead to an output line. When the output is turned on and
applies a ground, the coil of the relay will be energized and will turn the relay on. The output line
can "sink" (apply a ground) of about 150 milliamps. Connecting an output line directly to a power
supply and turning it on will destroy the output driver IC. Make sure that whatever you are turning
on and off draws less than 150mA.
The output lines can be turned on and off with Commands 093 and 094. You can recall whether a
line is currently on or off with Command 095. If you want to send a custom message when you
turn an output on or off, program one of the user macros to send the message you want, execute
Command 038 (to suppress the rest of the CW responses), and then turn the output line on or off.
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