Siemens RS-485 - Manual (Page 6)

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Siemens Building Technologies CC1A7865.1en
HVAC Products 31.10.2002
Checksum (CRC16)
The checksum (CRC16) is used to detect transmission errors.
If the evaluation reveals an error, the relevant device will not respond.
CRC = 0xFFF
CRC = CRC XOR ByteOfMessage
For (1 to 8)
CRC = SHR (CRC)
if (flag to the right = 1)
then
CRC = CRC XOR
0xA001
else
while (not all ByteOfMessage edited)
+
The low byte of the checksum will be transmitted first.
Data query:
Reading 2 words from address 6 (CRC16 = 0x24A0)
0B 03 00 06 00 02 A0 24
CRC16
Reply:
(CRC16 = 0x6105)
0B 03 04 00 00 42 C8 61 05
Word 1 Word 2 CRC16
The following functions for the device will be available:
Function number Function
0x03 / 0x04 Reading n words (n £ 12)
0x06 Writing 1 word
0x10 Writing n words (n £ 2)
Calculation
Example