Emerson PNC001-A Series User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 4
GFK-2222AK October 2019
CPU Operation 80
4.1.1.1 Major Phases in a Typical CPU Sweep
Phase
Activity
Housekeeping
The housekeeping portion of the sweep performs the tasks necessary to prepare for the
start of the sweep. This includes updating %S bits, determining timer update values,
determining the mode of the sweep (Stop or Run), and polling of expansion racks.
Expansion racks are polled to determine if power has just been applied to an expansion
rack. Once an expansion rack is recognized, then configuration of that rack and all of its
modules are processed in the Controller Communications Window.
Input Scan
During the input scan, the CPU reads input data from the Genius Bus Controllers and input
modules. If data has been received on an EGD page, the CPU copies the data for that page
from the Ethernet interface to the appropriate reference memory. For details, see
PACSystems and RX3i TCP/IP Ethernet Communications User Manual, GFK-2224.
Note: The input scan is not performed if a program has an active Suspend I/O function
on the previous sweep.
Application
Program Task
Execution
(Logic Window)
The CPU solves the application program logic. It always starts with the first instruction in
the program. It ends when the last instruction is executed. Solving the logic creates a new
set of output data.
For details on controlling the execution of programs, refer to PACSystems RX3i and RSTi-EP
CPU Programmer’s Reference Manual, GFK-2950 .
Interrupt driven logic can execute during any phase of the sweep. For details, refer to
PACSystems RX3i and RSTi-EP CPU Programmer’s Reference Manual, GFK-2950 Section 2.
A list of execution times for instructions can be found in Appendix A:.
Output Scan
The CPU writes output data to bus controllers and output modules. The user program
checksum is computed.
During the output scan, the CPU sends output data to the Genius Bus Controllers and
output modules. If the producer period of an EGD page has expired, the CPU copies the
data for that page from the appropriate reference memory to the Ethernet interface. The
output scan is completed when all output data has been sent.
If the CPU is in RUN Mode and it is configured to perform a background checksum
calculation, the background checksum is performed at the end of the output scan. The
default setting for number of words to checksum each sweep is 16. If the words to
checksum each sweep is set to zero, this processing is skipped. The background
checksum helps ensure the integrity of the user logic while the CPU is in RUN Mode.
The output scan is not performed if a program has an active Suspend I/O function on the
current sweep.

Emerson PNC001-A Series Specifications

General

Brand	Emerson
Model	PNC001-A Series
Category	Controller
Language	English