Common Driver Parameters

[OPC] Parameter

Allowable Values

Default Value

Description

Block

5 to 256

255

A value (bytes) used by the Plant SCADA I/O server to determine if two or more packets can be blocked into one data request before being sent to the OPC driver. For example, if you set the value to 10, and the I/O Server receives two simultaneous data requests (one for byte 3, and another for byte 8) the two requests are blocked into a single physical data request packet. This single request packet is then sent to the I/O device, saving on bandwidth and processing.

Delay

0 to 300

0

Period (in ms.) to wait between receiving a response and sending the next command to the I/O server.

MaxPending

1 to 1024

250

Maximum number of pending commands that the Plant SCADA OPC driver holds ready for immediate execution.

Polltime

0 to 300

1000

Polling service time (in milliseconds) at which cached data is updated. Recommended to be at least twice that of the value used in the Citect.ini [Alarm]ScanTime parameter.

Retry

0 to 8

0

Number of times to retry a command after a timeout.

Timeout

0 to 32000

3000

Milliseconds to wait for a response before considering a write or polling request to be invalid and displaying an error message in Plant SCADA.

Watchtime

0 to 128 (seconds)

15

Frequency that the Plant SCADA OPC driver uses to check the communications link to the OPC system and attempts to bring offline units back online. Also determines the frequency of STATUS_UNIT commands to the driver. See Configuring Redundancy.