MP270B touch screen set/reset bit.

Hello,

I have a button set a bit while button is down and reset a bit when button is released.
The question is if someone presses and releases the button quickly does the plc see the bit set for one scan and then reset on the next scan or does the plc see it as only a reset of bit?
Would the touchscreen set the bit , wait for a scan from the PLC and then do a reset of the bit on the next scan?

Thank you,
Merlin Knight

I'm not familiar with your particular HMI. Most offer a momentary button with a dwell time that may be adjustable (typical is 1/2 second). If that is not available, have the HMI set the bit when pressed, and let the PLC reset the bit after it has scanned it as being on. Chances are that the HMI can set and reset the bit before the PLC has a chance to scan it. The update time for the communication between the HMI and the PLC is a factor. If the HMI is a remote IO interface, then the PLC may see the states of all the bits during every housekeeping cycle. In the latter case, the scan time of the PLC may be a factor.

The HMI will not send both a set and a reset command to the PLC if the keypress is too short.

Best way to make certain that a button is "seen" by the PLC and also do not "hang" is to use set from the HMI, evaluate the bit in the PLC, and then reset it in the PLC (like OkiePC suggest).