adccommunitymod (AutomationDirect) asked a question.
Created Date: February 25,2003
Created By: C R Williams
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Anyone have experience with this operator interface panel? I'm using it with a DL260 CPU, "VGA " port. The sample programs all work well, so I don't have hardware or pointer issues. The problem is that some - or even most - of the messages don't display when sending a sequence of (PLC triggered) messages to the panel. In this case there's no user switch action (ie releasing the switch) to use to send the zero value to the panel (as shown in the tutorial examples). Sending it (zero) from the ladder program didn't work at all, even using a pair of contacts to make a two state 'ready-to-write ' circuit (Step 1 write message #; step 2 write 0). I think it might be something to do with the relatively long time the panel takes to respond over a 9600 baud link, when compared with the PLC scan cycle time of about 5ms, so that it doesn't see the message number, only the zero. If I put a 100ms timer (delay) in the ladder after writing the message # but before sending the zero it works some of the time. If I increase the delay to 250ms it works all the time. I'm reluctant to base a production design on an empirical result like this. So, does anyone know the real operational parameters for writing to this panel? Does it handshake at all? Is there a "Ready for data " or "data accepted " flag you can use? Or is it just a case of waiting long enough? How long is long enough? Hope you can help.
Created Date: February 25,2003
Created by: C R Williams
Anyone have experience with this operator interface panel? I'm using it with a DL260 CPU, "VGA " port.
The sample programs all work well, so I don't have hardware or pointer issues.
The problem is that some - or even most - of the messages don't display when sending a sequence of (PLC triggered) messages to the panel. In this case there's no user switch action (ie releasing the switch) to use to send the zero value to the panel (as shown in the tutorial examples). Sending it (zero) from the ladder program didn't work at all, even using a pair of contacts to make a two state 'ready-to-write ' circuit (Step 1 write message #; step 2 write 0).
I think it might be something to do with the relatively long time the panel takes to respond over a 9600 baud link, when compared with the PLC scan cycle time of about 5ms, so that it doesn't see the message number, only the zero. If I put a 100ms timer (delay) in the ladder after writing the message # but before sending the zero it works some of the time. If I increase the delay to 250ms it works all the time.
I'm reluctant to base a production design on an empirical result like this.
So, does anyone know the real operational parameters for writing to this panel? Does it handshake at all? Is there a "Ready for data " or "data accepted " flag you can use? Or is it just a case of waiting long enough? How long is long enough?
Hope you can help.
Created Date: March 07,2003
Created by: C R Williams
Tech support confirmed that you need a delay.
I found that this works: to write a "real " message, first set a "not ready " flag (contact) and send the message. Next wait 250ms, then write a "zero " message, and wait another 250ms before clearing the "not ready " flag. With this logic, if you ensure that the plc respects the "not ready " flag, (waits for it to clear before writing to the EZ Text display) then the EZ Text unit will always respond to the next plc message . It would be nice to shorten this delay, as a half second "lockout " is noticeable, but I can't get any definite (quantifiable) answers. A 100ms delay appears too short to be safe.
C R Williams