Crimson 3.0 Data Tag Data Source Access

I'm taking some lumps as I'm test driving a G3 terminal that's talking over Ethernet I/P with a CompactLogix PLC. I had first developed three or four screens with a full compliment of tags and promptly discovered that I could not get any communication between the G3 & PLC.

Next, I created a stripped down G3 database with a simple pushbutton, data entry and data display and stripped the PLC program down to the simple logic to handle said HMI primatives. I set a flag tag to 1 upon entry complete for my data entry so that the PLC would know new data was entered. (I'm used to PanelView notify/handshake bits and this was the most reasonable facsimilie in Red Lion). I then cleared this bit within the PLC.

I had issues with the "notify" bit not changing state after the first time data was entered. It turns out that because I had set the access of all my "write" bits to Write Only, the G3 would not set the bit again as it thought the bit was alread set. Tech Support talked me through changing the access to Read and Write to eliminate this issue.

Along with issuing a "caveat emptor", I wanted to ask if there is a similar issue with setting my access of my indicator flag tags to Read Only. I originally set my tags as read only or write only thinking that this would help speed up comms and eliminate programming mix ups. So much for that plan! Should I avoid all instances of Read Only & Write Only access? I'd prefer to only revamp my tag database only once, so any help would be appreciated.

Thanks in advance.

The "Write Only" mode is the only one that's ever caused me trouble, so I rarely use it anymore. I use "Read Only" quite often with no problems.

Thanks John. That's good to know. What advantages have you seen with using Read Only as opposed to Read and Write?

My usual practice is to make all tags "Read and Write" unless I know for certain that I'd never want to modify the value from the HMI, in which case I use "Read Only." I do this mainly as an extra layer of protection in case someone is tinkering with the program down the road. I doubt if there's any difference in communication speed between the two types of tags.