Interfacing EPICS IOCs With Allen Bradley PLCs Applications

Interfacing EPICS IOCs With Allen Bradley PLCs • Applications • Recent enhancements • Backwards compatibility • Reliability

EPICS device and driver support for Allen Bradley DF 1 protocol • Originally written for (and funded by) the KECK observatory • Recently updated for APT high power RF and personnel safety subsystems

DF 1 Driver Applications • IOC host architecture neutral – runs on PC, VME, and VXI IOCs • Point to point serial communication • Allen Bradley Data Highway communication – Allen Bradley KF 2 standalone – Data Link DL PC low cost ISA card

Recent Enhancements • Support for Allan Bradley PLC 5 architecture • Output tracking • DF 1 server • Others

Support for Allan Bradley PLC 5 architecture • PLC 5 addressing – Thanks to Eric Bjorklund for improved ASCII address parser • PLC 5 protocol – Data type safe R/W – Elements in files • Improved access control granularity

Output Tracking • IOC initialization does not block for Initial output value query completion – Output records in invalid / undefined alarm state until this query completes • Output records track changes occurring in PLC (they are processed) – Potential side effects when output records have forward links

DF 1 server • Allan Bradley PLCs see EPICS records as elements in files in a PLC 5 on DH+ • Reduced latency • Occurs when record addresses data highway node number of IOC

Other Enhancements • Specification of independent scan rate for each PLC 5 file • Each serial link or Data Highway may be assigned a different local node address • “drv. Serial” does not delete tasks when a link drops out

Backward compatibility • Continue to support original addressing and protocol of older PLCs – additional testing required for this version • Driver no-longer aborts a write in the queue so that it can be combined with another subsequent write

Reliability • This driver has been supporting the APT high level RF and window test systems since the beginning of the calendar year • The driver has been very reliable on this very lightly loaded PLC 5 system • Now have operational experience with Allen Bradley Data Highway

Getting a copy of the DF 1 protocol driver described here • KECK (Allan Honey) is the distribution point but I have not yet sent them a copy of this version

In Memory Communication with VME Resident Allen Bradley PLC 5? • Contact Eric Bjorklund (LANL LANSCE-6) for his driver • Both the DF 1 driver (described here) and Eric’s VME driver use the same common PLC 5 enhanced device support

Conclusions • The Allen Bradley DF 1 device / driver support has been upgraded to support PLC 5 s, output tracking, and DF 1 server operation. • It has been very reliable under continuous production, but lightly loaded, operation of the APT high power RF system.