Specifications

Section 9. CR1000 Programming

9-17

Scan determines how frequently instructions in the program are executed:

EXAMPLE 9.9-2. CRBASIC Code: Scan Syntax

'Scan(Interval, Units, BufferSize, Count)

Scan(1,Sec,3,0)

ExitScan

Scan has four parameters:

Interval is the interval between scans.

Units is the time unit for the interval. Interval is 10 ms < = Interval < = 1 day.

BufferSize is the size (number of scans) of a buffer in RAM that holds the raw

results of measurements. When running in Pipline mode, using a buffer allows

the processing in the scan to lag behind measurements at times without

affecting measurement timing.

Count is number of scans to make before proceeding to the instruction

following NextScan. A count of 0 means to continue looping forever (or until

ExitScan). In the example in EXAMPLE 9.9-2, the scan is 1 second, three

scans a

re buffered, and measurements and data storage continue indefinitely.

9.10 Program Timing: Slow Sequence Scans

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. When no measurements need to be

spliced, the scan will run independent of the fast scan, so slow sequences with

no measurements can run at intervals ≤ main scan interval (still in 100mS

increments) without skipping scans. When splicing, checking for skipped slow

scans is done after the first splice is complete rather than immediately after the

interval comes true.

In sequential mode, all instructions in the slow sequences are executed as they

occur in the program according to task priority.

Slow sequence scans are declared with the SlowSequence instruction and run

outside the main program scan. They typically run at a slower rate than the

main scan. Up to four slow sequences scans can be defined in a program.

Background calibration is an automatic slow sequence scan.