Communication System Manual
UPS System: HIPULSE E
(Modbus/Jbus Interface) Description of Protocol
(04/07)
Page 5-3
5.3.1 CRC Calculation Notes
The CRC (Cyclical Redundancy Check) is calculated according to the specifications of the MODBUS RTU protocol
using the CRC16 function (refer to Modicon documentation).
CRC is a word calculated by the transmitting device and placed at the end of the message sent. The receiver recalculates
CRC on the basis of the data received and checks that it corresponds to the CRC received. If the two values do not
correspond an error message is given.
The calculation procedure is as follows:
1. A hexadecimal value FFFF is calculated in a starting register referred to as CRC.
2. The first byte of the message is carried out using the low byte of the CRC, and the result is positioned in the CRC
register.
3. The CRC register is shifted to the right by one bit (toward the less significant bit - LSB), and a zero is put in the
position of the most significant bit (MSB). The LSB is examined.
4. If LSB=0, step 3 is repeated. If LSB=1, an exclusive OR of the CRC register with the hexadecimal value A001 is
applied.
5. Steps 3 and 4 are repeated until 8 shifts have been carried out. At this point, an entire byte has been processed.
6. Steps 2 through 5 are repeated with the successive byte, until all bytes have been examined.
The value container in the CRC register is the message CRC, which will be correctly positioned at the end of the
message.
5.3.2 Data Format Notes
- HEX Hexadecimal format in 1 or 2 bytes
(eg. value 1000 = 0x03E8 -> low byte = 0xE8 high byte = 0x03)
- HEX NIBBLE Hexadecimal Nibble format in 2 or 4 bytes
(eg. value 1000 = 0x03E8 -> low byte = 0x38, 0x3E, 0x33, high byte = 0x30)
- ASCII ASCII format in 1 or more bytes
(eg. Serial Number = ‘1234567890A’ -> low byte = 0x31,0x32,0x33, .. , 0x39,0x30,0x41)
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