3.2 Function Modules
Data Logging
3-80
Scan Setting Guidelines
This section describes guidelines for the scan settings based on when data is logged.
If Logging Is Synchronous with the Scan
The general logging overhead is given below. Set the scan setting to a value that is larger than this value.
Note: These overhead values are for word data without an application. Set the scan setting according to the application
usage conditions (number of registers to log, register types, ladder programs, etc.).
This timing chart illustrates the logging process when performed synchronously with the scan.
The logging processes for sampling the data and writing it to a file are performed within the scan cycle.
Therefore, the scan cycle (time period A in the figure on the previous page), must be set to a value greater
than the current scan time (time period B in the figure on the previous page).
If the scan cycle is shorter than the current scan time, a Scan Time Over Limit error will occur and the
count of SW00044 (High-speed Scan Over Limit Counter) or SW00046 (Low-speed Scan Over Limit
Counter) will be incremented. This can also cause a Watchdog Error (E.001) or cause the CPU Unit to go
down.
Set the scan time so that it is long enough to log the number of registered data items.
If Logging Is Asynchronous with the Scan
The scan setting for logging asynchronously with the scan should be set as given below.
Note: These values are for word data without an application. Set the scan setting according to the application usage con-
ditions (number of registers to log, register types, ladder programs, etc.).
This timing chart illustrates the logging process when performed asynchronously with the scan.
Data Items
1 to 8
9 to 60
61 to 64
Storage
Location
In the built-in RAM
disk
1.0 ms
1.5 ms
2.0 ms
USB memory
Due to the large overhead, USB memory cannot be used to log synchro-
nously with the scan.
Storage Location
Scan Setting Guidelines
In the built-in RAM disk
0.250 ms or longer
USB memory
0.500 ms or longer
DWG.H
High-speed or
low-speed scan
A: Scan cycle
B: Current scan time
Logging
(file writing)
This process samples
target data and loads it
into a logging buffer.
This process writes
data that was sampled
during the scan to the
log file.
Logging
(data
sampling)
Logging
(file writing)
DWG.H or
DWG.L
Logging
(data
sampling)
