Rockwell Automation 1785 PLC-5 User Manual download pdf (Page 49)

1785-UM022C-EN-P - February 2008

Planning to Use Your ControlNet PLC-5 Processor 2-11

Clearing the PCSC New Data and PCSC Overflow Bits

If it is crucial to maintain the integrity of the PCSC overflow bit after

new data has arrived while clearing the PCSC new data and overflow

bits. Then do the following:

1. Disable process control sample complete by setting the PCSC

enable bit for the connection to zero.

When process control sample complete is disabled, the system

will not modify the new data and overflow bits while you clear

them.

2. Clear the PCSC new data and the PCSC overflow bits.

3. Re-enable process control sample complete by setting the

connection’s PCSC enable bit back to one.

Considerations When Using PCSC

When using scheduled ControlNet 1.5 communications to analog I/O

(such as map entries) and you are using the PID instruction in the

PLC-5/15, then you should do the following:

• the analog module must be set up to use RTS (Real Time Sample)

mode

• set your analog RPI (Repetitive Packet Interval) to be at least

twice the RTS time

• your ladder program needs to set the PCSC enable bit

• your ladder program needs to use the PCSC done bit to condition

the execution of the PID instruction

• the PID loop update must equal the RTS rate

• your ladder program must use the PCSC overflow bit to take

appropriate action on an overflow condition

Understanding Scheduled

Connection Types

Scheduled connections are made to I/O devices such as I/O adapters

and to peer-to-peer devices such as other controllers.

There are some common scheduled connection types made from the

ControlNet PLC-5 to other Allen-Bradley products that are detailed

in the following section. These scheduled connection types have

certain behaviors and limitations that you must understand before

configuring the connections. The ControlNet PLC-5 can also make

scheduled connections to products not manufactured by

Allen-Bradley. Refer to the literature that accompanies those products

for information on their scheduled connection behavior.

Scheduled connection types made from the ControlNet PLC-5 to I/O

adapters can be made either to some or all of the discrete I/O on the

adapter (called a rack connection), or to individual modules (called a

module connection).

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