Bradley Smoker PLC-5 user manual Transferring Block Data, 6Communicating with Extended-Local I/O

8-6Communicating with Extended-Local I/O

The time in ms that it takes to scan extended-local I/O chassis depends on the number of 1771-ALX adapter modules and the number of extended- local I/O racks. The formula used to calculate the total time to scan extended-local I/O chassis is:

extended-local I/O scan time = (0.32 ms x A)+(0.13 ms x L)

where:

A= the number of 1771-ALX modules and

L= the number of racks in the extended-local I/O system

EXAMPLE

If you have three 1771-ALX modules in three chassis and a total of 4 racks, the total time is calculated as follows:

extended-local I/O scan time = (0.32 ms x 3)+(0.13 ms x 4)

extended-local I/O scan time = 1.48 ms

housekeeping time = 1.48 ms (extended-local I/O) + 4.50 ms(other housekeeping)

housekeeping time = 5.98 ms

Transferring Block Data

Requests for block-transfer data occur during the logic scan. Concurrent with the execution of the program logic, block-transfer requests are forwarded to the appropriate 1771-ALX adapter module(s) and data is transferred.

A1771-ALX adapter module may start block-transfer operations to multiple slots and have block-transfer data transactions on-going in parallel within the I/O chassis.

The block-transfer duration shown above does not affect logic scan time. This transfer of data occurs concurrent with execution of program logic.

Block-transfer duration is the time interval between the enabling of the block-transfer instruction and the receipt of the done bit.

Publication 1785-UM012D-EN-P - July 2005