Channel Scanning Sequence - Automation Direct DL405 User Manual

5–10
F4–08AD 8-Channel Analog Input
Channel
Scanning
Sequence
Before you begin writing the control program, it is important to take a few minutes to
understand how the module processes and represents the analog signals.
The F4-08AD module supplies one channel of data per each CPU scan. Since
there are eight channels, it can take up to eight scans to get data for all channels.
Once all channels have been scanned the process starts over with channel 1.
There are ways around this. Later we'll show you how to write a program that will get
all eight channels in one scan.
Unused channels are not processed, so if you select only two channels, then each
channel will be updated every other scan.
Scan
Read inputs
Execute Application Program
Read the data
Store data
Write to outputs
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.
Scan N
Channel 1
Scan N+1
Channel 2
. .
. .
. .
Scan N+7
Channel 8
Scan N+8
Channel 1