Checksum (Crc16); Calculation - Siemens RS-485 User Manual

Checksum (CRC16)

Calculation

Example
6/14
Siemens Building Technologies
HVAC Products
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
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
Reply:
(CRC16 = 0x6105)
0B 03 04
The following functions for the device will be available:
Function number
0x03 / 0x04
0x06
0x10
00 06 00
00 00
Word 1
Function
Reading n words (n £ 12)
Writing 1 word
Writing n words (n £ 2)
else
02 A0
CRC16
42 C8 61
Word 2 CRC16
24
05
CC1A7865.1en
31.10.2002