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2 Protocol description
Error
Measuring range underflow (Underrange)
Measuring range overflow (Overrange)
Other invalid value
2.6
Detection of bus errors
A bus error will be signaled if the device has an RS422/485 interface and a Modbus telegram is not re-
ceived for at least 10 s.
In the event of a malfunction, the power controller can thus switch to a configurable replacement value,
because the failure of the master means the setpoint value specified via Modbus is missing.
This behavior can be deactivated by setting the Modbus device address of the power controller to 0.
2.7
Checksum (CRC16)
Transmission errors are detected with the aid of the checksum (CRC16). If an error is detected during
evaluation, the device concerned does not respond.
Calculation principle
CRC = 0xFFFF
CRC = CRC XOR BytesOfMessage
For (1 to 8)
while (not all BytesOfMessage processed);
Example
Data request: read two words starting at address 0x00CE
(CRC16 = 0xA592)
07
03
Response: (CRC16 = 0xADF5)
07
03
12
CRC = SHR(CRC)
if (flag shifted to the right = 1)
then
CRC = CRC XOR 0xA001
00
CE
00
02
04
00
00
41
Word 1
Word 2
Error code for float values
0xFF800000 (Negative Infinity)
0x7F800000 (Positive Infinity)
0x7FC00000 (Not a Number)
else
A5
92
CRC16
C8
AD
F5
CRC16
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