Mitsubishi Electric MELSEC iQ-R Series User Manual page 46

■Head pointer and latest pointer
The storage location of the oldest data and the latest data in CH1 Logging data (Un\G10000 to Un\G10999) can be checked
with the following buffer memory areas.
Buffer memory area
CH1 Head pointer (Un\G434)
CH1 Latest pointer (Un\G435)
• When the number of collected data points is less than 1000
CH1 Head pointer
= 0
CH1 Latest pointer
= 5
• When the number of collected data points is 1001 or greater
CH1 Latest pointer
= 4
CH1 Head pointer
= 5
The head pointer does not change until CH1 Logging data (Un\G10000 to Un\G10999) becomes full after the logging start
(fixed to 0).
The head pointer moves by one point when CH1 Logging data (Un\G10000 to Un\G10999) becomes full and overwriting the
data starts from the start address.
■Checking logging data without stopping the logging operation
Logging data can be checked during the logging operation with 'CH1 Head pointer' (Un\G434), 'CH1 Latest pointer'
(Un\G435), and 'CH1 Number of logging data' (Un\G436).
To check logging data during logging operation, follow the precautions below because logging data may be refreshed while
data is being read out.
• Set the cycle to 'CH1 Logging cycle setting value' (Un\G537) so that data checking and reading surely complete before
logging data is refreshed. If the logging cycle is short, logging data may be refreshed during data checking and reading.
• After obtaining the logging data which needs to be checked, monitor the variation of the head pointer and the number of
logging data, and obtain logging data just after the stored value has changed.
• If the data refreshed and the data being checked do not synchronize due to the relationship between the logging cycle and
the scan time of the CPU module, adjust the logging cycle.
Stop the logging operation when the logging data needs to be checked without paying attention to the logging cycle. (
Page 45 Stopping the logging operation)
1 FUNCTIONS
44
1.10 Logging Function
Description
The buffer memory address of the oldest data in CH1 Logging data (Un\G10000 to Un\G10999) can be
checked with this buffer memory area. The offset value (0 to 999) counted from the start address of
CH1 Logging data (Un\G10000 to Un\G10999) is stored.
The buffer memory address of the latest data in CH1 Logging data (Un\G10000 to Un\G10999) can be
checked with this buffer memory area. The offset value (0 to 999) counted from the start address of
CH1 Logging data (Un\G10000 to Un\G10999) is stored.
Address 0 the oldest
Address 1
Address 2
Address 3
Address 4 the latest
Address 5
Address 998
Address 999
Address 0
Address 1
Address 2
Address 3
the latest
Address 4
the oldest
Address 5
Address 998
Address 999