EtherIP Driver Kay Kasemir, July 2009

2Managed by UT-Battelle for the U.S. Department of Energy EtherIP … is an EPICS driver/device support module … allows EPICS records to read/write tags from AllenBradley PLCs via ethernet – Control Logix with ENET module – Compact Logix also seems to work … works with vxWorks, RTEMS, Linux … is used by SNS, SLAC, … with 100s of PLCs – SNS: Conventional facilities, High-power RF, vacuum, water, personnel protection system, cryogenics, …

3Managed by UT-Battelle for the U.S. Department of Energy Protocol Details Basic ControlNet-over-Ethernet, EtherNet/IP protocol – Connect to PLC’s ENET module – Read serial number – Route messages to ‘controller’ (the PLC’s CPU) Allen-Bradley extensions – Read/write public ladder logic ‘tags’ – Combine multiple tag read/write requests into one message

4Managed by UT-Battelle for the U.S. Department of Energy Simple Example Startup File drvEtherIP_init() drvEtherIP_define_PLC("plc1", " ", 0) Record record(ai, ”plc_tag_4") { field(SCAN, "1 second") field(DTYP, "EtherIP") field(INP, SomeArrayTag[4]") field(PREC, "3") } Record record(ao, ”plc_tag_5") { field(SCAN, ”Passive") field(DTYP, "EtherIP") field(INP, SomeArrayTag[5] S 1") field(PREC, "3") }

5Managed by UT-Battelle for the U.S. Department of Energy Arrays are preferred N records connected to N tags “sensor1_current”, “sensor2_current”, “sensor4_voltage”, … N separate ‘read’ commands Driver tries to combine them into one network request, but still N different ‘reads’ Better: In ladder logic, create array with alias tags and have records read the array elements “sensor1_current”  array[0], “sensor2_current”  array[1], “sensor4_voltage”  array[2], … Driver will read array[0…Max] in one ‘read’ – Max = highest requested array element

6Managed by UT-Battelle for the U.S. Department of Energy Output records Usually SCAN=Passive When processed, will mark tag to be updated, driver will then ‘write’. Remaining time, driver reads the tag and updates record on change This was designed to allow both an IOC and PanelView to access the same tag

7Managed by UT-Battelle for the U.S. Department of Energy Issues Older ENET firmware would hang for 15 minutes every ~800 days PLC has buffer of about 500 bytes – Driver will combine pending read/write requests into message of up to 500 bytes for each the ‘request’ and the expected ‘response’, issuing multiple requests of 500 bytes each as needed. – The self-enforced limit of the driver is configurable. Actual limit of the PLC is not known and seems to change with versions. – Best to assume e.g. 450