CPU Specifications
and Operation
4–11
CPU Specifications and Operation
CPU Operation
Achieving the proper control for your equipment or process requires a good
understanding of how DL05 CPUs control all aspects of system operation. There are
four main areas to understand before you create your application program:
S CPU Operating System — the CPU manages all aspects of system
control. A quick overview of all the steps is provided in the next section.
S CPU Operating Modes — The two primary modes of operation are
Program Mode and Run Mode.
S CPU Timing — The two important areas we discuss are the I/O
response time and the CPU scan time.
S CPU Memory Map — DL05 CPUs offer a wide variety of resources,
such as timers, counters, inputs, etc. The memory map section shows
the organization and availability of these data types.
At powerup, the CPU initializes the
internal electronic hardware. Memory
initialization starts with examining the
retentive memory settings. In general, the
contents of retentive memory is
preserved, and non-retentive memory is
initialized to zero (unless otherwise
specified).
After the one-time powerup tasks, the
CPU begins the cyclical scan activity. The
flowchart to the right shows how the tasks
differ, based on the CPU mode and the
existence of any errors. The “scan time” is
defined as the average time around the
task loop. Note that the CPU is always
reading the inputs, even during program
mode. This allows programming tools to
monitor input status at any time.
The outputs are only updated in Run
mode. In program mode, they are in the off
state.
Error detection has two levels. Non-fatal
errors are reported, but the CPU remains
in its current mode. If a fatal error occurs,
the CPU is forced into program mode and
the outputs go off.
YES
Power up
Initialize hardware
Initialize various memory
based on retentive
configuration
Update input
Service peripheral
PGM
Mode?
RUN
Execute program
Update output
Do diagnostics
OK
NO
NO
Fatal error
Force CPU into
PGM mode
OK?
Report error, set flag
register, turn on LED
YES
Update Special Relays
CPU Operating
System
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