Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 113)

Programming
Chapter 3
3Ć70
Transfer 8 - The processor reads the status block with the ready bit W58
B12 reset to 0 and the load/enter complete bit W61 B13 set to 0. This
indicates that the buffered loop constants are being used to perform PID
control.
When the load/enter sequence is complete, The PID module
automatically sets itself for a dynamic block transfer or dynamic/status
toggle sequence initiated by using program.
NOTE: Loop 1 and loop 2 constants can be transferred to the PID
module and stored for future use. Later, when the enter bit is transferred,
any change in the dynamic block that are required for use with the new
loop constants should be transferred when the enter bit W01 B03 is set to
1. If transferred before the enter bit, the dynamic block changes will be
enabled without the corresponding changes to the loop constants.
Dynamic block values except for bits W01 B15, B14, B12, B11 are
implemented when transferred. The four bits and the loop constants
require a load/enter sequence to be completed before they can be
implemented.
The general concepts required for programming the PID module have
been explained in the previous sections. The following sections provide
additional information for applying these concepts in specific situations.
Section titled Load/Enter Sequence for Loop 1 operation explains the
changes which are required if only loop 1 is programmed.
Section titled Periodic Block Transfer explains the technique of
performing block transfers initiated by the status monitor byte or by
a block transfer watchdog timer.
Section titled Block Transfer Timing explains module block transfer
timing and system scan timing.
Load/Enter Sequence for OneĆLoop Operation
All references to the various block transfer sequences so far have assumed
2-loop operation. when the PID module is selected for loop 1 only
operation by setting W01 B15 to 1, the initial power-up load/enter
sequence is shortened. After loop 1 values are received (transfer 3 in
Figure 3.22) the read transfer will not prompt loop 2 but will prompt the
dynamic block instead. In effect, transfers 4 and 5 are skipped and the
Programming Considerations