The Data Field; The Lrc Field; The Eof Field; The Ready Field - Siemens SIMATIC TI505 User Manual

The Data Field

The LRC Field

The EOF Field

The Ready Field

SIMATIC TI505/TI500 MODNIM User Manual

Table 2-1 Modbus Functions Supported

Code Type
01 Read Coil Status
02 Read Input Status
03 Read Holding Register
04 Read Input Register
05 Force a Single Coil
06 Write a Single Register
07 Read Exception Status
08 Execute Diagnostics
11 Get Communications
Event Counter
12 Get Communications
Event Log
15 Write Multiple Coils
16 Write Multiple Registers
17 Report Slave I.D.
Note: The highlighted function codes (5, 6, 8, 15, and 16) are supported by Broadcast mode,
for which no response is returned.
The Data field contains the information needed by the specified node to
perform the required operation, or the information returned by the node to
the host computer. The data is in multiple bytes, with two ASCII character
bytes representing a hexadecimal value (1 . . . 9 and A . . . F or a . . . f).
The Longitudinal Redundancy Checking (LRC) is the method employed by
ASCII mode to ensure that the message transmitted by the host is the same
as the one that arrives at the secondary (and vice versa). The characters are
passed to a mathematical algorithm creating a checksum of 2 characters in
length that can be duplicated at either end for comparison. The calculation
of this checksum is described in the Modbus Protocol Reference Manual.
The End of File (EOF) marker, CR (carriage return) indicates the end of the
data and is the point up to which the LRC is generated.
The Ready field, LF (line feed) indicates that the sender is now ready for
any reply. This character can be changed using Function Code 08, with
Diagnostic code 03. Unless there is a compelling reason to change this
character, it should be left as the default value (LF).
Description
Get current status of a group of coils.
Get current status of a group of discrete
inputs.
Get current values from holding registers.
Get current values from input registers.
Change the state of a logic coil to On or Off,
forced On or forced Off, or unforced.
Write a value into a holding register.
Get the 8 internal status coil values.
Send diagnostic tests to a slave.
Enable the success or failure of a query to
be determined.
Get the communications log for Modbus
network transactions.
Change a number of consecutive coils.
Write values into a series of consecutive
holding registers.
Get the slave type and the condition of its
run light.
Modbus Commands 2-3