【文章內(nèi)容簡介】 odic reconnects. Per default, the driver bines requests for array elements into one array transfer from the first to the highest requested element. This leads to a significant reduction in transfer times, but might have side effects: The IOC will always write the whole array whenever more than one element has been changed by output records. If the same PLC array has been modified by another source (PanelView display) since the last transfer, the IOC is unaware of these changes and will overwrite them. An array transfer is also sizelimited by the aforementioned PLC buffer limit. The record configuration allows separate array element transfers as a workaround for these cases. For output records, the driver sends a CIP_Write_Data message whenever the record is processed. Otherwise it will periodically read the tag from the PLC and update the output record if the value on the PLC differs from the one in the record. The driver keeps statistical information (error counts, last/minimum/maximum transfer time) for each scan list. Analog input records allow access to these values. One problem arose with BOOL arrays since they are transferred as DINT values. For an analog record, a tag of “test [5]” is interpreted as addressing the 5th element of tag “test”. When this is applied to a BOOL array, the result would be the 5th DINT, containing bits 160191. So for binary records, all array access is assumed to target BOOL arrays, and “test [5]” would be transformed in a request to DINT[0], bit 5. This software has been tested on 68K, PPC and Pentium IOCs. The lower driver layer handles the different byte order. In addition, a simple mandline program is available for Unix and Win32 that allows read and write access to PLC tags as a debugging aid. 6 PERFORMANCE For the following, an MVME2100 CPU with a 100baseTwork interface municated to the PLC with its 10baseT connection via a dual speed hub. Another office PC and a Linux file server were connected to the same hub. Network utilization was generally below 2%. On average, 11 milliseconds are required to transfer a single tag, be it a scalar REAL, BOOL or DINT, an array of 15 REAL or 352 BOOL values. Since the EPICS driver bines multiple requests up to the PLC buffer limit, about 15 tags, each with a 15character name, can be read in one transfer of about 20 ms while the separate transfers would require more than 160 ms. In an attempt to simulate a mon application, an IOC was configured with 352 binary input records, scanning the elements of a BOOL array at 10Hz, and 120 analog input records, scanning three 40element REAL arrays at 2 Hz. Since Ether is not deterministic, these transfer rates vary over time due to collisions on the work, resulting in a transfer time histogram as shown in Fig. 1. Figure 1: Transfer times sampled over 3 days. On average, the whole BOOL array transfer was handled in 15ms, all REAL arrays were transferred in 25ms, so that the records could easily be updated at the chosen scan rate. In these measurements, the “System Overhead Time Slice of the PLC was set to 10%. After increasing it to 50% and connecting the CPU and PLC to a work switch, the average times for a single tag are reduced to 7ms. 7 CONCLUSION It is possible to use the published EtherNet/IP specification together with the openly available AllenBradley extensions to read and write tags on a ControlLogix system. The EPICS support is convenient to use. The record configuration can be changed at runtime。 transfers are automatically bined up to the PLC buffer limit. In contrast to other protocols, there is no need to define the affected tags as “produced” or “consumed”, nor does it require a workwide assessment of timing values for scheduling transfers as the original ControlNet did. Due to the nature of Ether, the exact transfer time varies. A switched work topology will help minimize variations. To reach the required throughput, values of interest should be arranged in arrays. To keep the ladder logic readable, intelligible tag names can be used to alias the meaningless transfer array elements. The published CIP service codes do not allow browsing of PLC tag names and type information, which would allow an even more userfriendly EPICS driver. With explicit messaging, each tag transfer is a roundtrip request. The tested version of the 1756ENET module does not support implicit messaging. Ideally the IOC could subscribe to the tags of interest and from then on receive asynchronous notification of changes or at least periodic updates, eliminating the need to poll. The current implementation, however, does already allow for a successful integration of ControlLogix systems into an EPICS environment REFERENCES [1] Rockwell Automation,“ControlLogix Selection Guide”,Publication 1756SG001AUSP from July 2021. [2] ControlNet International, Ltd, “ControlNet Specifications Release , Errata 2”, 2021. [3] Rockwell Automation, “Logix5000 Data Access”, from. , March 2021. [4] John K Munro, Jr., John C. Cleaves, KayUwe Kasemir, Ernest Williams, Delphy Nypaver, David Meyer, “Use of EPICS for HighLevel Controls of the SNS Conventional Facilities”, ICALEPCS 2021, San Jose, November 2021. [5] R. Stevens, “UNIX Network Programming”, Prentice Hall, 1990. 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