How to monitor the variable status on HMI

How to monitor the variable status on HMI

Hello, I got a problems during send value from HMI to PLC. The plc can not recieve the value from HMI. I do not know which place has problems. So I want to know how to monitor the variable status on PC or HMI, then i will know the varible status changed or not.:(

This is a migrated post! Originally posted on 29.02.2012 by user cypress329. Please be aware that information can be outdated.