Ethernet protocol description

Frame

Frame is composed by 4 fields:

• Node ID. It is used to identify the destination device.
  Value from 1 to 15 points to an axis whereas value 0 points to communication parameters.

• Header. It includes the master and slave commands

• Config data. Contains data from configuration access. If data is higher than 4 words, fragmentation is applied (see below).

• Cyclic data. Contains data from cyclic access. This field is by default disabled.

• CRC. CRC-CCITT (XModem) polynomial is used.
  

  CRC parameter	Value
  Width	16 bits
  Polynomial	0x1021
  Initial value (seed)	0x0000

  
  

Configuration access

Configuration access is the name used to identify acyclic / asynchronous requests from master to slave. This access type doesn't use the cyclic data field.

Addressing

Address field from the header is used to indicate the register to be accessed of the servo drive dictionary. The maximum supported registers are 2048 (11 bits) so the first bit of the field is reserved for future use and must be kept to 0.

Commands

The protocol is based on master-slave communication and all the commands sent by a master are confirmed by the slave, indicating the result of the operation. So every configuration is composed by two frames: Request from master to slave, and reply from slave to master. The available commands are:

Master commands

• Read Access 0b001. It is used to get a value from a drive register. Slave must reply with an ACK or Error on read (see below)

  Simple read example

  Read access to register 0x10

  NodeID		Header			Config data	CRC
  Reserved	Subsystem	Address	Command	Pending frame
  0x000	0x1	0x010	0b001	0	0	See this guide
  0x 01 00 02 01 00 00 00 00 00 00 00 00 XX XX

  
  

  
  

• Write Access 0b010. It is used to set a value of a drive register. Slave must reply with an ACK or Error on write (see below)

  Simple write example

  Write access to register 0x10

  NodeID		Header			Config data	CRC
  Reserved	Subsystem	Address	Command	Pending frame
  0x000	0x1	0x010	0b010	0	0x0006000000000000	See this guide
  0x 01 00 04 01 06 00 00 00 00 00 00 00 XX XX

  
  

  
  

• Get info command 0b000. It is used to obtain all the information of a register available on the MCB slave. Slave will reply with an ACK or Error. Data field from slave is coded in the next way:

  LSB (bits)	0..7	8..13	14..15	16..18	18..63	MSB (bits)
  	Size	Data type	Cyclic type	Access type	Reserved
  	Number of bytes	INT16 → 0	Config → 0	READ → 3
  		UINT16 → 1
  		INT32 → 2	Cyclic Tx (drive to master) → 1	WRITE → 5
  		UINT32 → 3
  		FLOAT → 4	Cyclic Rx (master to drive) → 2	READ/WRITE → 7
  		STRING → 5

  
  

  Get info example

  Getting information of register 0x011

  Master request

  Header			Config data	CRC
  Address	Command	Pending frame
  0x011	0b000	0	0x0000000000000000	See this guide
  0x01100000000000000000XXXX

  Slave reply

  Header			Config data	CRC
  Address	Command	Pending frame
  0x011	0b011	0	0x4102000300000000	See this guide
  0x01164102000300000000XXXX

  
  

  
  

• Idle command 0b111. It is used every time the master needs to send a frame without any configuration access.

Slave commands

• ACK access 0b011. Indicates that the request has been processed correctly

  Simple read example

  Successful reply to read access on register 0x10

  Header			Config data	CRC
  Address	Command	Pending frame
  0x010	0b011	0	0x0006000000000000	See this guide
  0x01060006000000000000XXXX

  
  

  
  

• Error on read 0b101. Indicates that the read request has not been executed correctly. Config data includes an error code to indicate the reason.

  Simple error on read

  Error reply to read access on register 0x10

  Header			Config data	CRC
  Address	Command	Pending frame
  0x010	0b101	0	0x0607001000000000	See this guide
  0x01090607001000000000XXXX

  
  

  
  

• Error on write 0b110. Indicates that the read request has not been executed correctly. Config data includes an error code to indicate the reason.

  Simple error on write

  Error reply to write access on register 0x10

  Header			Config data	CRC
  Address	Command	Pending frame
  0x010	0b110	0	0x0607001000000000	See this guide
  0x010C0607001000000000XXXX

  
  

  
  

• Idle command 0b111. It is used to indicate that slave reply is still being processed. It is used if configuration access is done when cyclic mode is enabled. See configuration access over cyclic section.

Error access codes

The possible error codes when a wrong access is detected are:

Data field

Data field contains the data from a read or write request. It is sent word by word (independent of the used physical layer) and in LSW (least significant word first). Whenever it is possible, the words are sent in MSB (Most significant bit first).

Data extension

If the data field is higher than 4 words (for example for ID registers that contains strings) the message might be extended to up to 256 words.

An extended configuration frame is generated indicated by the pending frame bit. When this bit is enabled, the first word of the configurration data contains the extended data number of bytes.

By default, the slave will try to send 512 bytes of extended data, but this behavior is configurable through request frame, writing the amount of bytes to receive as extended part in the config data: