DL205 Analog Manual, 7th Edition Rev. D
6-10
Chapter 6: F2-04RTD 4-Channel RTD Input
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Channel Scanning Sequence for DL240, DL250-1 and DL260 CPUs
(Pointer Method)
If a DL240, a DL250-1 or a DL260 CPU is being used, all four channels of input data can be
captured in one scan. This is because the DL240/250-1/260 CPUs support special V-memory
locations that are used to manage the data transfer. This is discussed in more detail in the next
section on Writing the Control Program.
Analog Module Updates
Even though the channel updates to the CPU are synchronous with the CPU scan, the module
asynchronously monitors the analog transmitter signal and converts the signal to a 16-bit
binary representation. This enables the module to continuously provide accurate measurements
without slowing down the discrete control logic in the RLL program.
The time required to sense the temperature and copy the value to V-memory is 160ms
minimum to 640ms plus 1 scan time maximum (number of channels x 160ms + 1 scan time).
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Read the data
Store data
ReadInputs
Execute ApplicationProgram
Scan
WritetoOutputs
Ch 1, 2, 3, 4
Scan N
Scan N+1
Scan N+2
Scan N+3
Scan N+4
Ch 1, 2, 3, 4
Ch 1, 2, 3, 4
Ch 1, 2, 3, 4
Ch 1, 2, 3, 4
System With
DL240/250-- 1/260CPU
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