AB ControlLogix 5000 Ethernet EWEB Scan Time

devker

Member
Join Date
Apr 2007
Location
Pohang
Posts
11
Hi,All
I can't express my opinion well in English.
You can't understanding, I am very worried about my write.

I'm communtcation between AB EWEB module ControlLogix 5000 and VME using socket programming Ethernet.

We were proposed 460byte data size every 25ms send and received.

VME to PLC successful.
but,PLC to VME failed.

PLC side configuration two Task scan.
one - Continuous - normal program
two - Period(25ms) - PLC<->VME Communication program.

PLC write MSG

writeMSG.EN
----|/|-------------------------------- writeMSG ----------------

but, This MSG not execute every 25ms. The same TON Timer.
reality check time execute 50ms.

socketWriteTimer.DN
----|/|----------------------------------- socketWriteTimer -----
Preset 25
Accum
socketWriteTimer.DN
----| |----------------------------------- writeMSG -------------

I'm guess scan time timing AB PLC SOTS(System Overhead Time Slice 10%) and writeMSG.EN reset or socketWriteTimer.DN.

I'm propose every 25ms data send.

Will you give me some advice?
 
EWEB should be able to do it, I tested it while ago with 5ms task the allows it send MSG every 10ms

Just remember that any message takes two scans to execute: Message needs to see both OFF-ON and ON-OFF rung conditions to restart
So change periodic task to 12.5ms and you should be able to send it every 25 ms.
Just want to make sure you understand:
- DN bit on the Write message indicated that EWEB put data on the wire and not a delivery.
- It may take more than one scan for EWEB to complete message so may not get your 25 ms all the time.
- Message processing at 12.5ms may put heavy loat on you processor leaving little time to execute cont task and comms.
- In any case you should have SOTS at least 20% may be more
 
Thank you very much.

I can't begin to tell you how grateful I am.
Yor are an expert in the field.

Thank you very much.
 

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