PACSystemsâ„¢ RX3i and RSTi-EP CPU Reference Manual Section 4
GFK-2222AK October 2019
CPU Operation 114
4.10.3.1.6 I/O System Initialization
If the module is an input module, no further configuration is required. If the module is an
output module, the module is commanded to go to its default state. The output modules
default to all outputs off at power-up and in failure mode, unless configured otherwise.
A bus transmitter module is interrogated about what expansion racks are present in the
system. Based on the bus transmitter module’s response, the CPU adds those racks and
their associated slots into the list of slots to be configured.
Finally, the I/O Scanner performs its initialization. The I/O Scanner initializes all the I/O
controllers in the system by establishing the I/O connections to each I/O bus on the I/O
controller and obtaining all I/O configuration data from that I/O controller. This
configuration data is compared with the stored I/O configuration and any differences
reported in the I/O Fault Table. The I/O Scanner then sends each I/O controller a list of the
I/O modules to be configured on the I/O bus. After the I/O controllers have been
initialized, the I/O Scanner replaces the factory default settings in all I/O modules with any
application-specified settings.
4.10.3.2 Power-Down Sequence
System power-down occurs when the power supply detects that incoming power has
dropped for more than 15ms.
4.10.3.3 Power Cycle Operation with an Energy Pack
Energy Packs offer distinct advantages over batteries:
a) significantly longer life cycles
b) they are more reliable
c) flammability during shipment is not an issue
d) in their end-of-life phase, their decline is a lot more gradual.
The system design includes the ability of the CPU and the Energy Pack to monitor each
other in real time. This permits the user to monitor alarms and thereby determine when
to replace a capacitor pack. The capacitor pack is normally replaced while the CPU is
powered on, giving it time to charge up before any subsequent loss of power. Users
should target periods which are expected to be free from electrical events, such as
thunderstorms, to carry out such work. Capacitor packs may also be replaced while power
is off.
When power is lost, the Energy Pack supplies current and maintains voltage levels for a
period of time sufficient to permit the connected CPU to save all dynamic memory to
non-volatile memory.
When power is restored, the CPU will not start running its application until the Energy
Pack signals that it is fully charged. The CPU will then resume operation using the
contents of memory retained at the previous loss of power event. The Energy Pack
charges continuously during normal operation.
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