EtherIP Driver

1
EtherIP Driver

• Kay Kasemir,
• kasemirk_at_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 PLCs ENET module
• Read serial number
• Route messages to controller (the PLCs 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, _at_plc1 SomeArrayTag4")
field(PREC, "3")
Record record(ao, plc_tag_5") field(SCAN,
Passive") field(DTYP, "EtherIP")
field(INP, _at_plc1 SomeArrayTag5 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 ? array0,sensor2_current
  ? array1,sensor4_voltage ? array2,
• Driver will read array0Max in one read
• Max highest requested array element

6
Output records

• Usually SCANPassive
• 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