adccommunitymod (AutomationDirect) asked a question.
Created Date: March 31,2005
Created By: JimR
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I'm talking to a master PLC with an eztouch through ethernet. The master is talking to a number of slaves. I'm using control relay C0 to turn on a relay Y0 in a slave via the touch panel. This works fine using a WX instruction in the master. I also want to turn on an indicator on the panel when a switch on the slave is closed so am using C1 as the control relay to turn on the indicator using an RX instruction. Since both C0 and C1 are in O40600 I seem to have troubles doing both an RX and WX instruction on the same location. If I do the RX first I read the wrong value into the C0 in the master. If I do the WX first I write the wrong C1 into the slave.I'm using stage programming so the RX and WX are in subsequent stages. The simple solution is to use C20 for the indicator which is in O40601 but because I have a lot of PLCs I'm afraid of running out of control relays this way. Any ideas?
Created Date: April 01,2005
Created by: bcarlton
You have found THE SOLUTION. In the master assign a word for reading and one for writing for each slave PLC. Make sure it's this way in the master and in the slaves. Also set up a pair for the display. You'll make your life a whole lot easier. I can see how you would be worried if you are using a DL05 as a master, it only has 32 words of 'C ' bits. The DL06 has quite a few more. What are you using?
Created Date: April 02,2005
Created by: JimR
Thanks bCarleton. Yes I'm using the DL06. I ended up using separate words for reads and writes and it works fine. Are there any shorcuts I should know about when using RX and WX? I'm using stage programming and If writing and reading to 27 PLCs this means a lot of stages. 1 for each read and 1 for each write. I guess the trick is to try to use consecutive memory locations for the reads and writes to minimize the stages required?
Created Date: April 02,2005
Created by: bcarlton
I guess the trick is to try to use consecutive memory locations for the reads and writes to minimize the stages required?
You got it. Doing one read of consecutive locations and one write per PLC will give you the shortest update time.
Created Date: March 31,2005
Created by: JimR
I'm talking to a master PLC with an eztouch through ethernet. The master is talking to a number of slaves. I'm using control relay C0 to turn on a relay Y0 in a slave via the touch panel. This works fine using a WX instruction in the master. I also want to turn on an indicator on the panel when a switch on the slave is closed so am using C1 as the control relay to turn on the indicator using an RX instruction. Since both C0 and C1 are in O40600 I seem to have troubles doing both an RX and WX instruction on the same location. If I do the RX first I read the wrong value into the C0 in the master. If I do the WX first I write the wrong C1 into the slave.I'm using stage programming so the RX and WX are in subsequent stages. The simple solution is to use C20 for the indicator which is in O40601 but because I have a lot of PLCs I'm afraid of running out of control relays this way. Any ideas?