Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 130)

Calculating Program Timing
Chapter 9
9-13
Category Words of
Memory 1
Time ( µ s)
Integer or
Floating Point
False
Time ( µ s)
Floating point
True
Time ( µ s)
Integer
True
Title Code
Miscellaneous END end negligible negligible 1
TND temporary end negligible 15
AFI always false 15 13
ONS one shot 28 30 2Ć3
DTR data transitional 41 41 4Ć7
BTD bit distributor 77 14 6Ć11
PID PID loop control 608 34 5Ć9
BTR block transfer read See Block Transfer BTR, BTW chapter
BTW block transfer write
MSG message See Message MSG chapter
W = number of elements acted on per scan
N = 2 x (number of integer file addresses) + 8 x (number of floatingĆpoint file addresses) + 6 x (number of timer, counter, or control N 2 x (number of integer file addresses) + 8 x (number of floating point file addresses) + 6 x (number of timer, counter, or control
file addresses) + ( number of conversions between integer and floating point formats)
1
Use the smaller number if all addresses are below word 4096; use the larger number if all addresses are above 4096.
Use program constants in compare, compute, and file instructions to
improve instruction execution times. Integer constants and floating-point
constants execute in less than 1
µ
s. Note that if you program using
constants you must edit the program to change the constants. If you
program using data table addresses, you can change the values by simply
changing the value in the data table.
Directly Addressed Elements
Additional execution time for directly addressed elements depends on:
data types
location in memory, referenced to the beginning of all data files (output
file, word 0)
whether data is stored at the source or destination address
whether the instruction converts data
Table 9.P lists times to add to instruction execution times.
Program Constants
Direct and Indirect Elements