Emerson PNC001-A Series User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 4
GFK-2222AK October 2019
CPU Operation 110
4.10.1.2.2 Outputs
Some output modules have a configurable output default mode that can be specified as
either Off or Hold Last State. If a module does not have a configurable output default
mode, its output default mode is Off. The selected action applies when the CPU
transitions from RUN/Enabled to RUN/Disabled or STOP Mode, or experiences a fatal
fault.
At power-up, Series 90-30 discrete output modules default to all outputs off. They will
retain this default condition until the first output scan from the PACSystems controller.
Analog output modules can be configured with a jumper located on the removable
terminal block of the module. The jumper may be set to cause outputs to either default to
zero or retain last state.
4.10.1.2.3 Inputs
Input modules that have a configurable input default mode can be configured to Hold
Last State or to set inputs to 0. If a module does not have a configurable input default
mode, its input default mode is Off. The selected action applies when the CPU transitions
from RUN/Enabled to RUN/Disabled or STOP Mode, or experiences a fatal fault.
For details on the power-up and STOP Mode behavior of other modules, refer to the
documentation for that module.
4.10.1.3 Multiple I/O Scan Sets
Up to 32 I/O scan sets can be defined for a PACSystems CPU. A scan set is a group of I/O
modules that can be assigned a unique scan rate. A given I/O module can belong to one
scan set. By default, all I/O modules are assigned to scan set 1, which is scanned every
sweep.
For some applications, the CPU logic does not need to have the I/O information every
sweep. The I/O scan set feature allows the scanning of I/O points to be more closely
scheduled with their use in user logic programs. If you have a large number of I/O
modules, you may be able to significantly reduce scan time by staggering the scanning of
those modules.
A disadvantage of placing all modules into different scan sets appears when the CPU is
transitioning from Stop to Run. In that case, scan sets with a programmed delay are not
scanned on the first sweep. These modules' outputs are not enabled until the new data
has been scanned to them, perhaps many scans later. Therefore, there is a period of time
during which the user logic is executing and some modules' outputs are disabled. During
that time, outputs of those modules are in the module’s stop-mode state. Stop-mode
behavior is module-dependent. Some modules zero their outputs, some hold their last
scanned state (if any), and some force their outputs to a configured default value. When
the module's outputs are enabled, the module uses the last scanned value, which will
either be zero or the contents of the register the module uses to hold the corresponding
output values from the reference tables.

Emerson PNC001-A Series Specifications

General

Brand	Emerson
Model	PNC001-A Series
Category	Controller
Language	English