Siemens SIMATIC S7-300 Reference Manual page 343
Programmable logic controllers module data
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Special characteristic of parameter assignment to upper and lower limit values
The programmable limit values (triggers for hardware interrupt) differ for the AI 8
RTD from the range of values shown in Table 4-68.
The reason for this is that numerical methods in the module software for evaluating
the process variables prevent values up to 32511 from being reported in some
cases. The process input value at which a hardware interrupt for an underflow or
overflow occurs depends on the calibration factors for an individual channel and
can vary between the lower limits shown in the table below and 32511 (7EFF
Limit values should not be set at values higher than the minimum potential limit
values shown in the table below.
End-of-scan-cycle interrupt
By enabling the end-of-scan-cycle interrupt, you can synchronize a process with
the conversion cycle of the module. The interrupt occurs when the conversion of all
the enabled channels is complete.
Table 4-72 Content of the 4 bytes with additional information from OB40 during a hardware
Content of the 4 bytes with
additional information
Special
analog
analog
markers
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
interrupt or an end-of-scan-cycle interrupt
2 bits per channel to identify the range
Upper limit exceeded in
channel
Lower limit exceeded in
channel
End-of-scan-cycle event
Unassigned bit
7
6
5
4
2
2
2
2
7
6
5
4
7
6
5
4
Analog Modules
).
H
3
2
1
0
2
2
2
2
3
2
1
0
3
2
1
0
X
4-137
Byte
0
1
2
3
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