Latching I/O

Introduction
This article explains how to configure a momentary push button to function like a toggle switch through the Concurrent I/O. This method, commonly referred to as “latch” or “latching” I/O, which requires a basic understanding of how to modify Concurrent I/O using the Ladder Program or Ladder Editor.

Overview
Latching I/O is when a physical or digital signal retains its state (such as ON/OFF or Open/Closed) after being set, even if the control signal is removed or power is lost. Reversing the state requires a separate, opposing command. Latching I/O is used for applications that need to preserve status information, such as lighting control or equipment state monitoring. In contrast, non-latching (failsafe) I/O automatically returns to a default condition when power is removed. In this article, it will briefly show how a momentary button is wired. Also, how the Concurrent I/O was modified to trigger the LED light to turn ON when the button is pressed and then how the LED is latched to stay ON after the button is pressed. The Emergency Stop Status Signal (Relay #80026) will be used to turn OFF the LED light.

Setup

Wiring
In this example the momentary button is wired to the door interface kit on a YRC1000. The button is connected to breakout card CN309, port A5, that corresponds to General Purpose Input #5. The LED signal is connected to port A12 on CN309 breakout card, which corresponds to General Purpose Output #5. 

Figure 1 : CN309 Breakout Card on a YRC1000, showing how the button & LED are wired.

Ladder Program – Concurrent I/O

Before Latching I/O
In this article, the Ladder Program will be used to modify the Concurrent I/O to latch the momentary button. As mentioned before, the Concurrent I/O will first be modified, so that when the user presses the button, the LED will turn ON and then OFF. Depending on the system, the output signal tied to the LED will need to be broken out of a GSTR/GOUT command. Once that’s done, input signal #20035 can be tied in, to trigger the LED output signal #30035. This is shown below, in Figure 2:

Figure 2: The Concurrent I/O modified by the Ladder Program. External Input Relay #20035 triggers the LED Light (External Output Relay #30035) to turn ON.

After making the changes and compiling the Concurrent I/O, now when the button is pressed, the LED will light up only when it is pressed. This can be seen, in Figure 3:

Figure 3: The green button being pressed and the LED lighting up.

Latching I/O
Now to latch the LED output signal, 2 available signals need to be identified in latching the I/O. In this example Auxiliary Relay #75000 & #75001 are used to latch the LED output signal. NOTE: Verify that signals #75000 & #75001 are available in one’s specific system. Then at the bottom of the Concurrent I/O add the 2 rungs as shown below (Figure 4) to latch the LED output signal. 

Figure 4: The two rungs that will latch the input signal to trigger the LED output to stay ON until the E-STOP button is pressed.

Then navigate back to the rung where the External Input #20035 is used to trigger the LED output (#30035) and change the relays signal to #75000.

Figure 5: The rung being modified so that Auxiliary Relay #75000 triggers the Output Signal #30035. Signal #30035 is physically connected to the green LED light.

After compiling the Concurrent I/O, now the LED light will stay lit, until the E-STOP button is pressed.

Figure 6: Example of how the LED output signal is latched to stay ON until the E-Stop is pressed. The LED will light up again by pressing the green button.

Conclusion
This is the process to latch the LED on a momentary push button to function like a toggle switch through the Concurrent I/O. Modifying the Concurrent I/O can also be done using the Ladder Editor. Prior to wiring any external devices, reference YRC1000 or YRC1000micro manuals to wire correctly. Not doing some may damage the output or input signal of the YRC1000 or YRC1000micro. Depending on the user’s system, it being a YRC1000 or YRC1000micro controller, an NPN or PNP General Purpose I/O (GPIO) board, available I/O, and/or available memory in the Concurrent I/O, the configuration may differ from the example shown in this article. However, the underlying logic and approach remains the same.