Discrete I/O Overview

Discrete I/O are physical boolean inputs or outputs. General discrete I/O are available on the following modules:

RMC	Module	Details
RMC75	D8 Expansion module	8 discrete I/O, individually programmable as inputs or outputs.
RMC150	DI/O Module	8 outputs, 18 inputs. Fits in slots 0, 2, 3, 4, and 5.
RMC150	CPU Module	2 outputs, 2 inputs
RMC200	D24 Module	24 discrete I/O: 0-19 individually programmable as inputs or outputs, 20-23 are inputs.
	CPU20L Module	2 outputs, 2 inputs
	CPU40 Module	2 outputs, 2 inputs
	CA4 Module	4 Fault inputs, 4 Enable outputs
	CV8 Module	8 discrete I/O, individually programmable as inputs or outputs.
	Q4 Module	4 Home inputs, 4 Registration inputs
	U14 Module	4 discrete I/O, individually programmable as inputs or outputs, 2 Reg/Z inputs

Some of the discrete I/O have dedicated functionality but can easily be used as general-purpose I/O, such as those on the CA4 and Q4 modules, and the Reg/Z inputs on the U14 modules. Other modules have dedicated discrete I/O that is more difficult to use a general-purpose I/O, such as:

RMC	Module	Details
RMC75	MA1, AA1, QA1	1 Fault Input, 1 Enable Output
RMC75	MA2, AA2, QA2	2 Fault Inputs, 2 Enable Outputs

Using General Discrete I/O

See the Using Discrete I/O topic for details on implementing the uses of discrete I/O listed below. Tag names can be assigned to general discrete I/O.

Discrete inputs can be used for the following:

To start a User Program.
As part of the condition for the Conditional Jump link type in User Programs.
In the Expression (113) command in a User Program.
Inputs can be forced using the Discrete I/O Monitor in RMCTools.
If configured to do so, one input can control whether the controller is in Run Mode or Program Mode.
As Physical Limit Inputs.

Discrete outputs can be used for the following:

The outputs can be set with the Expression (113) command in a User Program.
The outputs can be set by writing to the address of the output in the RMC via a PLC, HMI, etc.
Outputs can be toggled using the Discrete I/O Monitor in RMCTools.

Outputs can be forced using the Discrete I/O Monitor in RMCTools.

Configuring the Discrete I/O

To configure the discrete I/O, use the Configuring Discrete IO topic.

Viewing the Discrete I/O

There are two ways to view the state of the discrete I/O:

Use the Discrete I/O Monitor in RMCTools.
Look at the LEDS on the module, if the module has LEDs.

Addressing Discrete I/O

See the Register Map for details on the addresses of the discrete I/O registers.

Discrete I/O points are represented as bits in the RMC. To address a bit, you must specify the bit in the register that contains it. Not all host controllers allow this, depending on the protocol. For example, addressing a bit in an F file using an Allen-Bradley protocol is not supported in many HMIs. Typically, specifying bits in any word is possible with most controllers using Modbus/RTU or Modbus/TCP. Notice that you may need to address the upper 16-bit portion of the 32-bit register in order to pick out the bits higher than 15.

In RMCTools, the discrete I/O addresses are shown in the IEC 61131-3 format:

RMC	I/O Addressing	Examples
RMC75	Inputs = %IXn Outputs = %QXn where n is the I/O number as displayed in the Discrete I/O Monitor.	%QX0 is output 0 %IX8 is input 8
RMC150	Inputs = %IXslot.n Outputs = %QXslot.n where slot numbering starts with 0 for the left-most module in the RMC150. n= the number of the input or output on that module.	%QX0.5 is output 5 in slot 0 %IX5.0 is input 0 in slot 5
RMC200	Inputs = %IXslot.n Outputs = %QXslot.n where slot numbering starts with 0 for the left-most module in the RMC200. n= the number of the input or output on that module.	%QX1.0 is output 0 in slot 1 %IX5.7 is input 7 in slot 5