Rockwell Automation 2711 MODBUS COMMUNICATIONS FOR PANELVIEW TERMINALS - Manual (Page 14)

Publication 2711-6.9 - March 2000
14 Modbus Communications for PanelView Terminals
Modbus Address Spaces The PanelView reads and writes data into other Modbus devices on
the same network. The Node Address specifies the device (node) and
the Address Type specifies the address space. The following address
types are supported:
•
Input Status (status of Modicon controller discrete input)
•
Output Coil (status of Modicon controller discrete output)
•
Input Register (contents of input register in Modicon controller)
•
Holding Register (contents of holding register in Modicon
controller)
Modbus devices can contain four distinct address spaces. Two spaces
are reserved for Coil data and two are reserved for Register data. The
PanelView terminal can read from any of the four address spaces.
However, the PanelView terminal can only write to the Output Coil
and Holding Register address spaces.
Coil Addressing
In Write Tags
If Output Coil address type is specified in a write tag, the data is
written to the Coil address using Modbus Function Code 5 (single coil)
or Function Code 15 (multiple coils).
In Read Tags
If either Coil address type is specified in a read tag, data is read from
the appropriate Coil address. For Input Status Coils, the status of the
discrete input is read using a Modbus Function Code 2. For Output
Coils, the status of the discrete output is read using Function Code 1.
Register Addressing
In Write Tags
If Holding Register address type is specified in a write tag, data is
written to the Register address using Modbus Function Code 6 (single
register) or Function Code 16 (multiple registers).
In Read Tags
If an Input Register or Holding Register is selected in a read tag, data
is read from the appropriate Register address using Modbus Function
Code 3 (holding register) or Function Code 4 (input register).