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EtherIP Driver

The .EtherIP.Driver.Kay.Kasemir module is an EPICS driver/device support that enables reading and writing tags from Allen-Bradley PLCs via Ethernet, compatible with Control Logix and Compact Logix. Supported operating systems include vxWorks, RTEMS, and Linux. Used by SNS and SLAC with various PLCs in conventional facilities such as high-power RF, vacuum systems, and cryogenics. The driver utilizes EtherNet/IP protocol for ControlNet-over-Ethernet communication with PLC's ENET module. Arrays are preferred for connecting multiple records to tags to optimize network requests, allowing faster tag reads and writes. The driver handles pending read/write requests by combining them into messages based on the PLC's buffer size limit. The driver's self-enforced limit is configurable, ensuring efficient communication between the EPICS system and Allen-Bradley PLCs.

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EtherIP Driver

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  1. EtherIP Driver Kay Kasemir, kasemirk@ornl.gov July 2009

  2. 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, …

  3. 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

  4. Simple Example Startup File drvEtherIP_init() drvEtherIP_define_PLC("plc1", "160.91.232.217", 0) Record record(ai, ”plc_tag_4") { field(SCAN, "1 second") field(DTYP, "EtherIP") field(INP, ”@plc1 SomeArrayTag[4]") field(PREC, "3") } Record record(ao, ”plc_tag_5") { field(SCAN, ”Passive") field(DTYP, "EtherIP") field(INP, ”@plc1 SomeArrayTag[5] S 1") field(PREC, "3") }

  5. 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

  6. 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

  7. 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

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