Bonfiglioli CM-232/CM-485/CM-485T Modbus Communication Manual



Bonfiglioli CM-232/CM-485/CM-485T Modbus Communication Manual

Document Fundamentals and Security 

Document positioning: Belongs to the supplementary document of the frequency converter operation manual; The complete set of documents includes a quick start guide, a complete operation manual, an application manual, and module installation instructions.

safety requirements

The module disassembly and assembly must completely cut off the main power supply of the frequency converter to prevent static electricity from damaging the circuit board; Only licensed electricians are allowed to operate.

The frequency converter operates with high voltage, and there is residual voltage in the bus capacitor after power failure.

Storage conditions: The original packaging should be dry and dust-proof, and stored without electricity for no more than 1 year.

It is prohibited to plug and unplug communication modules with power on.

Module Introduction

CM‑232：RS232， Point to point 1-to-1 communication, DB9 female port X310.

CM-485: RS485, DB9 interface; CM‑485T：RS485， 7-position plug-in terminal.

The RS485 bus can accommodate up to 247 frequency converter slave stations, with a master-slave architecture where only the master station initiates messages and the slave station does not actively send them.

Factory default protocol parameters: Protocol=VABus; Baud rate 19200; Verify EVENT even verification; Slave station address=1; Watch dog 413=0 (off).

Switching Modbus requires setting parameter 395:2=Modbus RTU; 3=Modbus‑ASCII； 0=VABus original factory protocol.

Note: Slot A is the KP232 adapter (for VPlus debugging software), slot B is the CM-232/485 module. When connecting CM-232/485 to PLC, VPlus software cannot use this port and must use KP232 adapter.

Module installation and removal

Power off, remove the upper and lower cover plates of the frequency converter, and access the Slot-B communication slot.

Install the PE grounding spring (M4 screw), insert the module into Slot-B and hear a click. Secure the module to the grounding spring with the M2 screw; Knock open the prefabricated opening on the top cover for the X310 connector to pass through, and restore the cover plate.

Disassembly: Loosen the M2 screw, use a small screwdriver to open the left and right buckles of the module, alternately pull out the module, remove the PE spring, and restore the cover plate.

ESD anti-static: Do not directly touch the PCB components on the back of the module.

Pin definition, bus terminal matching, cables 

1）CM‑232 DB9（X310）

Pin signal

2 RxD reception

3 TxD transmission

5 0V GND

The shell is shielded and connected to PE; the remaining pins are empty. A 1:1 direct shielded twisted pair cable is required.

2) CM-485 DB9 version X310

Pin signal

1 B

2 B '(parallel)

3 0V

5 +5V

7 A

8 A '(parallel)

The shell is shielded and connected to PE.

3) CM-485T Terminal Edition X310

Terminal signal

1 A

2 A 'parallel connection

3 B

4 B 'parallel connection

5 +5V

6 0V

7 PE shielding ground

Bus terminal resistor S1 dip code

The first and last nodes of the bus physics must open the terminal resistor S1=ON, and all the middle nodes must be OFF.

Prohibit the simultaneous use of onboard dialing code S1 and external active terminal circuits.

RS485 recommends twisted pair shielded cables with PE connections at both ends of the shielding layer; maximum bus distance corresponding to different baud rates: 2400bps=2400m; 19200bps=1200m； 115200bps=300m。

Start configuration parameters 

Parameter Number Parameter Name Description

10 Baud Rate Baud rate 2400~115200; After modification, software reset (parameter 34 written to 123) or power-off and power on are required for it to take effect

1375 Modbus Parity checksum 0=EVENT even; 1=ODD odd; 2=None without verification; The modification needs to be reset to take effect

1376 Modbus Address Slave Address 1-247; The modification takes immediate effect; 0 is the broadcast address, and there is no response to the broadcast

395 Protocol Select 0 VABus/2 RTU/3 ASCII

413 Watchdog watchdog timer 0 closed; 1-10000s; timeout report F2010 communication failure

The modification of baud rate and verification requires restarting the frequency converter; The modification of the station address takes effect immediately. Software reset method: Write parameter 34 to 123.

Detailed Explanation of Modbus Serial Protocol 

5.1 master-slave model

0: Broadcast address, write command to broadcast all slave stations, no response message; 1-247 independent slave stations.

Message structure: [Slave address] [Function code] [Data] [Verify CRC/LRC].

Exception message: Function code highest position 1 (+0x80)+Exception code.

5.2 Support Function Code (including Bangfeili Custom Extension)

Function code name and purpose

0x03 reads 16 bit hold register to read 16 bit inverter parameters; Only one register can be read at a time

0x06 Write a single 16 bit hold register and write a 16 bit parameter; One register at a time

0x64 (100) Custom read 32-bit parameter read long 32-bit parameter (non-standard Modbus)

0x65 (101) Custom write 32-bit parameter write long 32-bit parameter (non-standard Modbus)

0x08 Diagnostics Diagnostics reads communication error counter, reset counter

Address encoding rule (key) Modbus request starting address 16 bits: high 4 bits=dataset number (0-9), low 12 bits=internal parameter number of the frequency converter. Example: Parameter 372, Dataset 2 → Address=0x2174. Floating point/decimal parameters: Communication transmission uses amplified integers, such as 10.3A transmitting the value 103; 100.00Hz transmission of 10000.

5.3 Exception codes

Meaning of Exception Code

1 Illegal function code

2 illegal data addresses (parameters do not exist, number of registers ≠ 1)

3 Illegal data values

4. Equipment failure at the substation; Read parameter 11 to obtain detailed low-level errors

Parameter 11 VABus SST Error Register: Read detailed errors at the bottom layer (read-only), automatically reset after reading.

5.4 RTU and ASCII transmission modes

Modbus‑RTU

Character 11 bits; A frame interval of ≥ 3.5 characters is used to determine the start and end of the frame; CRC-16 checksum (low byte first sent); Higher transmission efficiency, commonly used in engineering.

If the character gap is greater than 1.5 characters, the message will be discarded directly.

Modbus‑ASCII

Frame start character colon:, end CR+LF; LRC verification; 7-bit data; The maximum allowable interval between characters is 1 second; Low bandwidth efficiency.

5.5 Timing and Watchdog

After receiving the message, the frequency converter should wait at least 10ms before replying; The host sends the next message at least 2ms apart; if the host does not receive a response within 500ms, it will be judged as timeout. When the CPU is under high load, the timeout will be greater than 500ms.

Watchdog 413: If there is no correct Modbus message within the set time when it is not 0, report fault F2010 RS232 485 watchdog fault; 0=Turn off the watchdog.

5.6 Dataset, RAM/EEPROM read-write mechanism (emphasis)

The frequency converter has 5 sets of data sets (0-4) for multiple parameter switching.

Dataset 0-4: Write and save to EEPROM (non-volatile storage) at the same time, EEPROM has a write life of about 1 million times; Prohibit cyclic high-frequency writing as it may burn the EEPROM.

Dataset 5-9: Only writes to RAM (volatile, lost during power failure), suitable for PLC to periodically issue control words and set frequencies.

Dataset 0 → RAM Address 5

Dataset 1 → RAM Address 6

Dataset 2 → RAM Address 7

Dataset 3 → RAM Address 8

Dataset 4 → RAM Address 9

Important: Control word 410, RAM given frequency 484, RAM percentage given 524, fixed use dataset 0 (RAM), will not be written to EEPROM.

Modbus Message Instance 

The document provides complete examples of RTU and ASCII:

Example of FC03 reading 16 bit parameters; Example of exception return.

FC06 Write 16 bit parameter example.

FC100 (0x64) reads 32-bit parameters.

FC101 (0x65) writes 32-bit parameters.

FC08 diagnosis: reset counter, read various communication statistics (total received messages, CRC errors, abnormal responses, overflow errors, etc.).

ACT inverter serial port control logic

Operate three core registers through Modbus:

410 Control Word control word (16 bits): Issue commands such as start stop, reset, and quick stop.

411 Status Word status word (16 bits): reads the bit status of the drive's running status, faults, warnings, reaching the given limit, etc.

484 Reference Frequency RAM: Given the RAM frequency (32-bit, -999.99~999.99Hz)

524 Reference Percentage RAM: Given percentage (32-bit, -300~300%)

The hardware enable S1IND (hardware terminal) has the highest priority, and the driver cannot be enabled solely by the bus control word. The hardware terminal must provide an enable signal.

Three control modes, selected by parameter 412 Local/Remote

Mode 0: Control via Contacts: All start and stop directions come from hardware digital inputs, and control word 410 is invalid.

Mode 1: Control via State Machine Control (DRIVECOM): Bus control word 410 implements the complete drive state machine; Standard servo/inverter bus control, supporting complete state jump, fault reset, and quick stop.

State machine: not ready → prohibit closing → ready closing → closed → enabled operation, quick stop activation, fault state.

Parameter 392 State transition5 defines the shutdown behavior when the enable switch is switched back to closed: 0 free sliding; 1. DC braking; 2 Slope shutdown.

Mode 2: Control via Remote Contacts Remote Virtual Terminal: Control word 410 simulates hardware DI input for each bit; Equivalent to mapping all digital inputs such as S1IND-S6IND to control word bits.

Given source mode (parameter 434 Ramp Setpoint ramp setting source)

1=Only internally given; 2=Given only bus RAM; 3=Internal given+bus given superposition. Readable actual value parameters: 228 internal reference, 282 bus reference, 283 ramp output reference frequency.

ACU (ACTION Cube) Control

ACU is a compact servo drive for Cube, also using 410 control words/411 status words/484/524 given. Differences:

The hardware safety enable is a dual channel STO safety terminal for STOA/STOB (S1IND/S7IND), which must be hardware effective, and the bus cannot replace hardware safety.

ACU supports external 24V control power supply; Modbus communication can still be maintained even when the main power is disconnected, and the status word bit4 (Voltage enabled) provides feedback on whether the main power supply is powered on.

The meaning of some bits in the state machine of the motion control mode (configuration 30=x40) has changed.

Key Parameter Index

The manual lists the communication related VAL actual value menu and PARA parameter menu; Key Points:

249 Active Data Set: The current active dataset;

Read the status of the DI terminal using 250 digital inputs;

260 Current Error Current fault code;

270 Warning bit encoded warning word;

414 Data Set Selection bus switching dataset;

637/638: Fast stop shutdown threshold and holding time;

632 DC braking time.

Appendix: Alarm and Fault Codes 

Warning (270): 16 bit encoding, overheating, Ixt overload, motor temperature, phase fault, V-band monitoring, etc.

Fault error code (260): F01 overload, F02 radiator overheating, F03 internal temperature, F04 motor temperature, F05 output short circuit, F07 bus voltage, F20 10: RS232 485 communication watchdog fault.

Attached ASCII code table 0x00-0x7F.