Mitsubishi Electric MELSEC iQ-R User Manual page 92

Data checking method
■Current logging read pointer
• The head pointer read from Logging data area (Un\G10000 to Un\G99999) with the interrupt processing is stored in 'CH1
Current logging read pointer' (Un\G444, Un\G445).
• The default value of 'CH1 Current logging read pointer' (Un\G444, Un\G445) is -1.
• Every time data is logged for the number of data points set in 'CH1 Logging read points monitor value' (Un\G448,
Un\G449), a value calculated by the following formula is stored in 'CH1 Current logging read pointer' (Un\G444, Un\G445).
CH1 Current logging read pointer = CH1 Latest pointer - CH1 Logging read points monitor value + 1
■Previous logging read pointer
• The value of 'CH1 Current logging read pointer' (Un\G444, Un\G445) at the timing when the previous read pointer detection
interrupt occurs is stored in 'CH1 Previous logging read pointer' (Un\G446, Un\G447).
• The default value of 'CH1 Previous logging read pointer' (Un\G446, Un\G447) is -1.
• 'CH1 Previous logging read pointer' (Un\G446, Un\G447) is used to detect the overlap of the logging read pointer detection
interrupt processing.
Ex.
The values to be stored in each pointer at every detection interrupt when the logging read detection starts with the setting
below
• 'CH1 Logging data points setting' (Un\G536): 100 (10000 points)
• 'CH1 Logging read points setting value' (Un\G547): 10 (1000 points)
Occurrence of read pointer
detection interrupts
When an interrupt has not occurred
First time
Second time
Third time

10th time
11th time
12th time
1 FUNCTIONS
90
1.14 Normal Logging Function
Buffer memory area
Previous logging read pointer
-1 (default value)
-1
0
1000

8000
9000
0
Current logging read pointer
-1 (default value)
0
1000
2000

9000
0
1000
Latest pointer
0 (default value)
999
1999
2999

9999
999
1999