Hello, I'm new to PLC programming and recently hit an I/O comm snag.
I'm using a DirectLogic 205 DL250 PLC with an InTouch 7.1 HMI. The I/O Server is Modbus. When the HMI is reading data from the PLC, everything is fine. I can also write data to V-memory (I use DirectSOFT to double check), so no problem there. But when I try to write data to the control relays, things get weird.
Here's what happens: I use a user input touch link in the HMI to turn on a CR tag, and the CR in the PLC does turn on like it's supposed to. I can see in DirectSOFT that the CR goes from OFF to ON and stays ON. But in the HMI, the CR tag goes from OFF to ON for a split second, then goes back to OFF. For some reason, after writing to the PLC, the HMI is not reading (or incorrectly reading) the status of that CR bit from the PLC.
When I disconnect the HMI from the PLC and repeat the process (to troubleshoot), the CR tag in the HMI stays ON, instead of going OFF like it did earlier. So is there a problem with the PLC? What can it be?
Any reply would be appreciated.
- Wing Fox
I'm using a DirectLogic 205 DL250 PLC with an InTouch 7.1 HMI. The I/O Server is Modbus. When the HMI is reading data from the PLC, everything is fine. I can also write data to V-memory (I use DirectSOFT to double check), so no problem there. But when I try to write data to the control relays, things get weird.
Here's what happens: I use a user input touch link in the HMI to turn on a CR tag, and the CR in the PLC does turn on like it's supposed to. I can see in DirectSOFT that the CR goes from OFF to ON and stays ON. But in the HMI, the CR tag goes from OFF to ON for a split second, then goes back to OFF. For some reason, after writing to the PLC, the HMI is not reading (or incorrectly reading) the status of that CR bit from the PLC.
When I disconnect the HMI from the PLC and repeat the process (to troubleshoot), the CR tag in the HMI stays ON, instead of going OFF like it did earlier. So is there a problem with the PLC? What can it be?
Any reply would be appreciated.
- Wing Fox