Configuring the CONTROL and DATABUF Parameters

Overview

The CONTROL and DATABUF output parameters define the operations of the MBP_MSTR function block. For the EtherNet/IP protocol, the structure of the CONTROL and DATABUF output parameters remains the same for all explicit messaging services.

Configuring the Control Parameter

Use MSTR operation 14 or 270 to send generic Modbus requests on the network. (These operation codes are not available on the Modbus Plus port or embedded Ethernet port on the CPU.)

The CONTROL parameter register contains these consecutive words:

Register	Function	Description
`CONTROL[0]`	operation	14 = unconnected 270 = connected
`CONTROL[1]`	detected error status	Holds the event code (read-only).
`CONTROL[2]`	data buffer length	Data buffer length, in words
`CONTROL[3]`	response offset	Offset for the beginning of the response in the data buffer, in 16-bit words Note: To avoid overwriting the request, make the response offset value greater than the request length `CONTROL[10]`.
`CONTROL[4]`	routing register	Specify a network destination node during data transfer: MSB: The most significant byte contains the source node address (for example, the slot number of the 140 NOE 771 •• or 140CRP31200 module). Exception: The value of the integrated Ethernet port on the CPU is 254 (FE h) regardless of the CPU slot number. Note: Only 1 Ethernet 140CRP31200 module can be used. LSB: The least significant byte contains the destination node address (for example, MBP on the Ethernet Transporter (MET) mapping index for the 140 NOE 771 •• or the drop number for the 140CRP31200).
`CONTROL [5]`¹	IP address	Each address contains 1 byte of the 32-bit IP address: high byte = byte 4 of the IP address (MSB) low byte = byte 3 of the IP address high byte = byte 2 of the IP address low byte = byte 1 of the IP address (LSB)
`CONTROL [6]`¹	IP address
`CONTROL[7]`	request length	length of the CIP request, in bytes
`CONTROL[8]`	response length	length of the response received, in bytes read only—set after completion
1. For example, the Control parameter handles the IP address 192.168.1.6 in the following order: Byte 4 = 192, Byte 3 = 168, Byte 2 = 1, Byte 1 = 6.

Configuring the Data Buffer

The DATABUF varies in size. It consists of contiguous registers that include—in sequence—both the CIP request and the CIP response. To avoid overwriting the request, confirm that the data buffer is large enough to contain both the request and response data.

Data Buffer:

Variable size: set in CONTROL[2]

CIP Request:

Request size: set in CONTROL[7]

CIP Response:

Starting position: set in CONTROL[3]

Response size: reported in CONTROL[8]

NOTE: If the response offset is smaller than the request size, response data overwrites part of the request.

The formats of the data buffer’s CIP request and CIP response are described in this table. (Both the request and response are structured in little endian order.)

Request
Byte offset	Field	Data Type	Description
0	Service	Byte	Service of the explicit message
1	Request_Path_Size	Byte	The number of words in the Request_Path field
2	Request_Path	Padded EPATH	This byte array describes the path of the request (including class ID, instance ID, etc.) for this transaction.
...	Request_Data	Byte array	Service-specific data in the explicit message request delivery (if none, this field is empty)
Response
Byte offset	Field	Data Type	Description
0	Reply Service	Byte	Service of the explicit message + 16#80
1	Reserved	Byte	0
2	General Status	Byte	EtherNet/IP General Status
3	Size of Additional Status	Byte	Additional Status array size—in words
4	Additional Status	Word array	Additional status
...	Response Data	Byte array	Response data from request, or additional detected error data if General Status indicates a detected error