DL205 Analog Manual, 7th Edition Rev. D
5-10
Chapter 5: F2-08AD-2, 8-Ch. Analog Voltage Input
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Channel Scanning Sequence for a DL240, DL250-1 or DL260 CPU
(Pointer method)
If either a DL240, a DL250-1, or a DL260 CPU are used, all eight channels of input data can
be collected in one scan. This is because the DL240, DL250-1 DL260 CPUs support special
V-memory locations that are used to manage the data transfer which is discussed in more detail
in the 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 12-bit
binary representation. This enables the module to continuously provide accurate measurements
without slowing down the discrete control logic in the RLL program.
For the vast majority of applications, the values are updated much faster than the signal
changes. However, in some applications, the update time can be important. The module takes
approximately 4 milliseconds to sense 95% of the change in the analog signal.
NOTE: This is not the amount of time required to convert the signal to a digital representation. The conversion to the digital
representation takes only a few microseconds. Many manufacturers list the conversion time, but it is the settling time of the
filter that really determines the update time.
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Read the data
Store data
ReadInputs
Execute ApplicationProgram
Scan
WritetoOutputs
Ch 1, 2, 3, ...8
Scan N
Scan N+1
Scan N+2
Scan N+3
Scan N+4
Ch 1, 2, 3, ...8
Ch 1, 2, 3, ...8
Ch 1, 2, 3, ...8
Ch 1, 2, 3, ...8
System With
DL240/250-- 1/
260CPU
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