Slave Address; Modbus Registers; Data Consistency - Emerson 2202 Advanced User's Manual

Parameter
Introduction
x.00 description format
The master must implement a message time out to handle transmission errors. This time out period must be set to the maximum slave response time
+ transmission time for the response.
Master request
6.1.2

Slave address

The first byte of the frame is the slave node address. Valid slave node addresses are 1 through 247 decimal. In the master request this byte indicates
the target slave node; in the slave response this byte indicates the address of the slave sending the response.
Global addressing
Address zero addresses all slave nodes on the network. Slave nodes suppress the response messages for broadcast requests.
6.1.3

MODBUS registers

The MODBUS register address range is 16bit (65536 registers) which at the protocol level is represented by indexes 0 through 65535.
PLC registers
Modicon PLCs typically define 4 register 'files' each containing 65536 registers. Traditionally, the registers are referenced 1 through 65536 rather than
0 through 65535. The register address is therefore decremented on the master device before passing to the protocol.
File type Description
1 Read only bits
2 Read / write bits
3 Read only 16bit register
4 Read / write 16bit register
The register file type code is NOT transmitted by MODBUS and all register files can be considered to map onto a single register address space.
All parameters in the drive are holding registers.
CT parameter mapping
All CT products are parameterized using the menu.param notation. Indexes 'menu' and 'param' are in the range 0 through 99. The menu.param is
mapped into the MODBUS register space as menu*100 + param.
To correctly map the parameters at the application layer, the slave device increments the received register address. The consequence of this
behaviour is that Pr 0.00 cannot be accessed.
CT MODBUS PLC
parameter register
X.Y 40000 + X x 100 + Y X x 100 + Y - 1
Examples:
Pr 1.02 40102
Pr 1.00 40100
Pr 0.01 40001
Data types
The MODBUS protocol specification defines registers as 16bit signed integers. All CT devices support this data size.
Refer to the section 6.1.8 Extended data types on page 20 for detail on accessing 32bit register data.
6.1.4

Data consistency

All CT devices support a minimum data consistency of one parameter (16bit or 32bit data). Some devices support consistency for a complete multiple
register transaction.
Commander SK Advanced User Guide
Issue Number: 9
Parameter Keypad and
display communications
minimum silence
period
Slave frame
frame detect
processing
Slave response time
Register address
Comments
(protocol level)
Pr 0.00
cannot be
accessed
101
99
0
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Serial CT Modbus PLC Ladder
RTU programming
Slave response
Time
Parameter Advanced parameter
CTSoft
x.00
minimum silence
period
Master request
New master request
can start here
descriptions
17