3.2 Function Modules
Data Logging
3-81
3
CPU Unit Functionality
The logging process for sampling the data is performed within the scan, while the process of writing the
data to a file is performed in background processing.
The background process is performed during the idle processing time of the scan. Therefore, the idle pro-
cessing time (time period A in the above figure) must be longer than the logging overhead (time period B
in the above figure).
If the logging overhead time is longer than the idle processing time of the scan, the file writing process can
run into the next scan and cause an over limit error. The number of over limit errors can be checked in the
over limit counter (SW24008).
Monitoring the Logging Execution Status
You can monitor the execution status of data logging by checking the system registers. Refer to the follow-
ing section for details.
−
Data Logging Execution Status (page 4-69)
Viewing the Log Data
To view the log data in a PC, the data that is stored in the RAM in the CPU Unit or USB memory device
must be transferred to the PC. Refer to the following section for details on data transfers.
DWG.H
DWG.L
DWG.H
High-speed scan
Current high-speed
scan time
This process samples
target data and loads it
into a logging buffer.
This process samples
target data and loads it
into a logging buffer.
Low-speed scan cycle
Current low-speed
scan time
A: Idle processing time
B: Logging overhead
Logging
(file writing)
The shaded portion shows
that the higher priority
processing is interrupting
lower priority processing.
This process writes data
that was sampled during
the scan to the log file.
Low-speed scan
Background
processing
High-speed scan cycle
Logging
(data
sampling)
Logging
(data
sampling)
Logging
(data
sampling)