Campbell CR800 Specifications download pdf (Page 16)

CR800 and CR850 Overview

is converted to a value determined by the processing included in the

instruction, and then the datalogger proceeds to the next instruction. Because

of this step-by-step instruction execution, conditional measurements are

allowed in sequential mode. The exact time at which measurements are made

may vary if other measurements or processing are made conditionally, if there

is heavy communications activity or other interrupts.

OV2.3.3 Slow Sequence Scans

The datalogger allows for one or more scans that are run outside of the

instructions placed between the Scan/NextScan instructions in the main

program. These scans, referred to as slow sequence scans, typically run at a

slower rate than the main scan. Up to four slow sequences can be defined in a

program (slow sequences are declared with the SlowSequence instruction).

Instructions in a slow sequence scan are executed whenever the main scan is

not active. When running in pipeline mode, slow sequence measurements will

be spliced in after measurements in the main program, as time allows. Because

of this splicing, the measurements in a slow sequence may actually span across

multiple main program scan intervals. In sequential mode, all instructions in

the slow sequences are executed as they occur in the program (see Task

Priority, below).

OV2.3.4 Task Priority

When considering the information above regarding pipeline and sequential

mode, you must also consider that some sequences in the program may have

higher priorities than other sequences in the program, and that measurement

tasks generally take precedence over all others. In addition, the priority of

sequences is different for pipeline mode and sequential mode.

When running in pipeline mode, measurement tasks have priority over all other

tasks. Measurements in the main program have the highest priority, then

background calibration, followed by any measurements in slow sequences that

may be defined. The execution of processing tasks are handled by a task

sequencer, and all tasks are given the same priority. When a condition is true

for a task to start running it is put in a queue (this true condition can be based

on time, the triggering of WaitDigTrig, the expiration of a Delay instruction, or

a ring on a COM port triggering communication). Because all tasks are given

the same priority, the task is put at the back of the queue. Every 10 msec (or

faster if a new task is triggered) the task currently running is paused and put at

the back of the queue, and the next task in the queue begins running. In this

way, all tasks are given equal processing time by the datalogger. The only

exception to this task switching queue is when a measurement task is triggered.

In most instances the processing task and the measurement task should be able

to run in parallel. However, if the datalogger is unable to complete a

measurement when the task sequencer is executing, the task will be interrupted

until the measurement is made.

When running in sequential mode, the datalogger uses a queuing system for

processing tasks similar to the one used in the pipeline mode. The main

difference when running a program in sequential mode is that there is no

prescheduled timing of measurements; instead, all of the instructions are run in

the order they occur in the program. A priority scheme is used to avoid

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Campbell CR800 Specifications Page 16

Comments to this Manuals

Campbell CR800 Specifications Page 16

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