Delta 1770-KF2, SLC-500, PLC-5 user manual Theory of Operation

			Powerful Solutions for Digital Plants
2	THEORY OF OPERATION
	As part of the serial interface port license, a standard Modbus protocol is installed on the
	DeltaV PSIC prior to customization. The PSIC needs to be flash upgraded from the
	Modbus protocol to the Allen-Bradley protocol before operation.
	The Allen-Bradley serial driver implements DF1 protocol. It communicates with PLC-3,
	PLC-5 or SLC5/XX devices on the DH+ network through either a 1785-KE or 1770-KF2
	communication modules. These modules convert the DF1 serial protocol to the DH+
	network protocol. The switch settings must be configured properly for the RS-232 or RS-
	422/485 prerequisite for proper operation.
	The Allen-Bradley Driver communicates with the PLC and updates emulated DeltaV I/O
	with the data received from the PLC. The primary functions of the driver are listed below:
	￿￿ Performs data and message handling between DeltaV and PLC-3 / PLC-5 / SLC5/XX.
	￿￿ Sends messages to PLC-3 / PLC-5 / SLC5/XX from DeltaV
	￿￿	Processes reply information and updates the corresponding emulated DeltaV I/O
		channels
	￿￿	Update emulated input	channel status and Data Block status to indicate the
		communication state of PLC-3 / PLC-5 / SLC5/XX.
	￿￿ Checks validity of messages received by PLC-3 / PLC-5 / SLC5/XX.
	Upon proper installation and configuration of the Allen-Bradley driver within the
	DeltaV/PSIC system, communications with a properly configured Allen-Bradley PLC-3 /
	PLC-5 or SLC5/XX may proceed.
	There are a maximum of 16 Datasets (DS) per port, with a total of 32 per PSIC. The
	maximum number of data elements per Dataset that can be supported by the PSIC
	depends on the data file type. Note that the number of supported Datasets does not
	change. The following table describes this correlation:
	Dataset Data File Type		Number of Data Elements
			or Registers
	Boolean		100
	Discrete		100
	8-bit signed integer		100
	16-bit signed integer		100
	32-bit signed integer		50
	8-bit unsigned integer		100
	16-bit unsigned integer		100
	32-bit unsigned integer		50
	Floating point		50
	String		1

The DeltaV PSIC is the master in all communications. It polls each input device and requests data values on a message by message basis. The output is performed when a new value is to be written to the devices. The PSIC constantly scans the configured input Datasets for new values and updates the database. Upon a change of value in the output Dataset, the PSIC will finish the current input scan and suspend the input process. It will service all the output requests before resuming the input process.

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