Rockwell-automation 1771-QA Stepper Positioning Assembly User Manual Manual de usuario descargar pdf (Pagina 64)

3–42 Programming and Operation

Publication 1771-UM002A–EN–P – May 2000

Processor Scan Time PS = (5ms/lK words) x (4K words) =

20ms.

Processor I/O Scan Time PIO = (0.5ms/rack number x (4

rack numbers) = 2ms

Number of Words Transferred = 64 (write) or 10 (read)

3. Calculate the block transfer times T for the write and read

operation.

T = 0.1 + (.075ms/word x 64 words)

= 0.1 + 4.8

= 4.9ms (write)

T = 0.1 + (.075ms/word x 10 words)

= 0.1 + .75

= .85ms (read)

4. Calculate the worst case system time ST between 2 consecutive

write block transfers.

The stepper controller module toggles to a read operation in the scan

following completion of the write operation.

ST = PS + PIO + T(1) + T(2) + T(3) + T(4) (writes)

PS + PIO + T(1) + T(2) + T(3) + T(4) (reads)

ST = 2PS + 2PIO + 4T (write) + 4T (read)

= 2(20) + 2(2) + 4(4.9) + 4(.85)

= 40 + 4 + 19.6 + 369

= 67 ms

This is the worst case time between two consecutive write block

transfers in the 4-chassis local configuration described in example

problem 2 (enabled stepper assembly in each chassis).

Mini-PLC-2/15 Controller

The program scan and I/O scan are consecutive and are considered as

a single processor scan. The Mini-PLC-2/15 scan time varies

typically from 18 to 24ms for a 1K program and one I/O rack. Each

block transfer module will be updated during a program scan.

The procedure for calculating the worst case time between transfers

can be done in three steps.

1. Write down the known facts and system values.

• Processor Scan time PS = 24ms

• Number of Words Transferred W default value of the module

2. Calculate the block transfer time T for the read and write

operation.

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Rockwell-automation 1771-QA Stepper Positioning Assembly User Manual Manual de usuario Pagina 64