Bradley Smoker PLC-5 user manual Controller Time, Minimum time to complete, Update Image

Maximizing System Performance C-11

To optimize your system layout for block-data transfers, use an arrangement similar to the following:

PLC

System Optimized for Block-Data Transfer

With this arrangement, a block-transfer to each BT module can occur in a single discrete I/O scan.

Adapter	BT	Maximum scan time	= 3 discrete scans + 3 block-transfers
			= 3D + 3BT
Adapter	BT
		Minimum time to complete
Adapter		a block-transfer to all modules		= 1 (3D + 3BT)
	BT			= 3D + 3BT

Controller Time

The controller time is the time needed to process the inputs and set the corresponding outputs. This controller time varies for different controllers and is based on input buffering, program scan, etc.

In a PLC-5 system, inputs are buffered between the I/O image table and the remote I/O buffer. The movement of inputs from the remote I/O buffer to the input buffer is asynchronous to the movement of data from the input buffer to the input image table.

Remote I/O Scan Loop Program Scan Loop

Rack 3

Rack 2

Rack 1

AdapterAdapter Adapter

Remote I/O Buffer

Input

Buffer

Data Exchange

x y

a b		Update
I/O Image
		I/O image
Table
		from input
		buffer
	Data
	Exchange
Processor-
Resident
Rack

Housekeeping

Immediate I/O 1

IOT (x)

IIN (y)

a

write outputs

b

read inputs

Logic

Scan

Publication 1785-UM012D-EN-P - July 2005