ProSoft Technology MVI69L-MBTCP - Manual (Page 115)

MVI69L-MBTCP ♦ CompactLogix Platform Reference
Communication Module User Manual
ProSoft Technology, Inc. Page 115 of 152
January 6, 2014
7.2.7 Preset Single Register (Function Code 06)
Query
This Function Code allows the user to modify the contents of a Modbus 4x range
in the server. This will write to a single register only. Any holding register that
exists within the controller can have its contents changed by this message.
However, because the controller is actively scanning, it also can alter the content
of any holding register at any time. The values are provided in binary up to the
maximum capacity of the controller unused high order bits must be set to zero.
When used with Server address zero (Broadcast mode) all Server controllers will
load the specified register with the contents specified.
Note Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
Th
e example below is a request to write the value ‘3’ to register 40002 in server
11.
Node
Address Function
Code Data Start
Point High Data Start
Point Low Preset Data
Register
High
Preset Data
Register
Low
Error Check
Field (2 bytes)
0B 06 00 01 00 03 CRC
Response
The response to a preset single register request is to re-transmit the query
message after the register has been altered.
Node
Address
Function
Code
Data Register
High
Data Register
Low
Preset Data
Register High
Preset Data
Register Low
Error Check
Field (2 bytes)
0B 06 00 01 00 03 CRC
7.2.8 Diagnostics (Function Code 08)
This Function Code provides a series of tests for checking the communication
system between a Client device and a server, or for checking various internal
error conditions within a server.
The function uses a two-byte sub-function code field in the query to define the
type of test to be performed. The server echoes both the function code and sub-
function code in a normal response. Some of the diagnostics commands cause
data to be returned from the remote device in the data field of a normal response.