Application Guide | iC2-Micro Frequency Converters
6.1.7.4.7 CRC Check Field
Telegrams include an error-checking field, operating based on a cyclic redundancy check (CRC) method. The CRC field checks the
contents of the entire telegram. It is applied regardless of any parity check method used for the individual characters of the telegram.
The transmitting device calculates the CRC value and appends the CRC as the last field in the telegram. The receiving device recalculates
a CRC during receipt of the telegram and compares the calculated value to the actual value received in the CRC field. 2 unequal values
result in bus timeout. The error-checking field contains a 16-bit binary value implemented as 2 8-bit bytes. After the implementation,
the low-order byte of the field is appended first, followed by the high-order byte. The CRC high-order byte is the last byte sent in the
telegram.
6.1.7.4.8 Coil Register Addressing
Introduction
In Modbus, all data is organized in coils and holding registers. Coils hold a single bit, whereas holding registers hold a 2 byte word (that is
16 bits). All data addresses in Modbus telegrams are referenced to 0. The 1st occurrence of a data item is addressed as item number 0. For
example: The coil known as coil 1 in a programmable controller is addressed as coil 0000 in the data address field of a Modbus telegram.
Coil 127 decimal is addressed as coil 007Ehex (126 decimal).
Holding register 40001 is addressed as register 0000 in the data address field of the telegram. The function code field already specifies
a holding register operation. Therefore, the 4XXXX reference is implicit. Holding register 40108 is addressed as register 006Bhex (107
decimal).
Coil Register
Table 35: Coil Register
Coil number Description Signal direction
1–16 Drive control word. Master to follower
17–32 Drive speed or setpoint reference range 0x0– 0xFFFF (-200% ... ~200%). Master to follower
33–48 Drive status word. Follower to master
49–64 Open-loop mode: Drive output frequency.
Closed-loop mode: Drive feedback signal.
Follower to master
Parameter write control (master to follower).
0 = Parameter changes are written to the RAM of the drive.
65
1 = Parameter changes are written to the RAM and EEPROM of the drive.
Master to follower
66–65536 Reserved. –
Drive Control Word (FC Profile)
Table 36: Drive Control Word (FC Profile)
Coil 0 1
01 Preset reference lsb
02 Preset reference msb
03 DC brake No DC brake
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