2-30 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
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Section 3: Power-Up and Power-Down Sequences
There are two possible power-up sequences in the Series 90-30 PLC; a cold power-up and a warm
power-up. The CPU normally uses the cold power-up sequence. However, in a Model 331 or
higher PLC system, if the time that elapses between a power-down and the next power-up is less
than five seconds, the warm power-up sequence is used.
Power-Up
A cold power-up consists of the following sequence of events. A warm power-up sequence skips
Step 1.
1.The CPU will run diagnostics on itself. This includes checking a portion of battery-backed
RAM to determine whether or not the RAM contains valid data.
2.If an EPROM, EEPROM, or flash is present and the PROM power-up option in the PROM
specifies that the PROM con tents should be used, the content s of PROM are copied into RAM
memory. If an EPROM, EEPROM, or flash is not present, RAM memory remains the same
and is not overwritten with the contents of PROM.
3.The CPU interrogates each slot in the system to determine which boards are present.
4.The hardware configuration is compared with software configuration to ensure that they are
the same. Any mismatches detected are considered faults and are alarmed. Also, if a board is
specified in the software configuration but a different module is present in the actual
hardware configuration, this condition is a fault and is alarmed.
5.If there is no software configuration, the CPU will use the default configuration.
6.The CPU establishes the communications channel between itself and any intelligent modules.
7.In the final step of the execution, the mode of the first sweep is determined based on CPU
configuration. If RUN mode, the sweep proceeds as described under “STOP-to-RUN Mode
Transition.” Figure 2-5 on the next page shows the decision sequence for the CPU when it
decides whether to copy from PROM or to power-up in STOP or RUN mode.
Note
Steps 2 thr ou gh 6 above do not apply to th e Series 90 Micro PLC. F or
information about the power-up and power-down sequences for the Micro, refer
to the “Power-up and Power-down Sequences” section of Chapter 5, “System
Operation,” in the Series 90 Micro PLC User’s Manual (GFK-1065).