3.3 Automatic Data Collection

BASEstar Classic device connection management has the ability to receive data values generated by plant devices without issuing a prior request. To use this unsolicited data collection capability, the devices and physical points must be correctly defined using BASEstar Classic software. For information on defining devices and data for unsolicited collection, refer to the BASEstar Classic Command Line Interface User's Guide.

Allen-Bradley PLCs are capable of sending unsolicited messages to an OpenVMS host. In order to generate unsolicited data, the ladder logic program for the Allen-Bradley PLCs must use the Allen-Bradley message instruction. The following components of the message instruction support unsolicited data:

• Address and size of the data to be sent
• Data Highway address of the communications controller to which the OpenVMS host is connected
• Destination (of the data to be sent) table address

The messages sent must be a PLC-2 protected or unprotected write instruction. The address is an octal PLC-2 address.

For SLC controllers use the 485CIF target device to send PLC-2 messages. Also for SLC controllers the destination address is specified as a decimal byte offset. This value must be converted to a word octal address to obtain the unsolicited ID to use for the message coming from the device.

The DAS for AB Data Highway Protocol uses the destination table address as the unsolicited ID. Because unsolicited ID's are numeric, the family of the destination device must be PLC-2. For further information about the message instruction, see the Allen-Bradley documentation of your specific device.

The DAS for AB Data Highway Protocol allows you to define BASEstar Classic device connection management physical points for collecting unsolicited data. When the device sends an unsolicited message to the OpenVMS host, the DAS for AB Data Highway Protocol forwards the message to BASEstar Classic device connection management. The maximum unsolicited message size allowed is 244 bytes. By default, the maximum unsolicited ID designation allowed is 127 (decimal). You can override this default by setting one of the following BASEstar Classic parameters.

PE	Parameter Name
AB	ILAN$AB_MAX_UNSOL_ID
AB2	ILAN$AB2_MAX_UNSOL_ID
AB3	ILAN$AB3_MAX_UNSOL_ID
AB5	ILAN$AB5_MAX_UNSOL_ID
SLC	ILAN$SLC_MAX_UNSOL_ID

The parameter must be within the range 1 - 65535.

Unsolicited messages are received in the DAS for AB Data Highway Protocol by posting an unsolicited read request for the device. When the device sends an unsolicited message to the DAS for AB Data Highway Protocol, the message is read and sent to BASEstar Classic device connection management and any interested applications. It is possible for the device to send another message before the first one has been processed. Only five unsolicited read requests are queued per device. If six messages are read in quick succession before any of the first five have been processed, the sixth message is discarded. The number of queued unsolicited read requests can be redefined by setting one of the following BASEstar Classic parameters:

PE	Parameter Name
AB	ILAN$AB_UNSOL_QUEUE_SIZE
AB2	ILAN$AB2_UNSOL_QUEUE_SIZE
AB3	ILAN$AB3_UNSOL_QUEUE_SIZE
AB5	ILAN$AB5_UNSOL_QUEUE_SIZE
SLC	ILAN$SLC_UNSOL_QUEUE_SIZE

There is no minimum or maximum number of read requests for the queue size.

For information on setting parameter values, refer to the BASEstar Classic Configuration and Tuning Guide.

3.3.2 Pollsets

BASEstar Classic device connection management physical points can be grouped together into pollsets to optimize data collection. Pollsets created for the Allen-Bradley PLCs have the following limitations:

• Physical points with different data types cannot be part of the same pollset. For example, a physical point of type WORD and a physical point of type BIT cannot be members of the same pollset. Physical points of the same data type with varying element counts can reside in the same pollset.
• Members of pollsets created for the PLC-3 must have identical context, section, and file values.
• Pollset members for PLC-5s and SLCs must have identical file numbers. PLC-5/250 pollset members must have identical module numbers.

For more information on physical points, refer to the BASEstar Classic Command Line Interface User's Guide.