User manual

Chapter 4 Configuration
Page 127 ©February 2009
4.14.2 Modbus Plus Addressing
Modbus Plus node addressing can be set using switches or via configuration software. To use the
switch address settings, the “Enable Switch Address” option in configuration software must be
selected, otherwise switch settings are ignored. NOTE – software address configuration is the
recommended option if use of the GDB Offset and Count parameters is required (see section
4.11.4).
Two sets of six switches are available: Node Address (S1, the left-most set of switches, closest to
the D-SUB connector), and Source Address (S2, the right-most set of switches). Address settings
for both switches use the same binary format illustrated in the table below.
1
MSB
2 3 4 5 6
LSB
Function
ON ON ON ON ON ON Node Address set to 1
ON ON ON ON ON OFF Node Address set to 2
ON ON ON ON OFF ON Node Address set to 3
--- --- --- --- --- ---
OFF OFF OFF OFF OFF ON Node Address set to 63
OFF OFF OFF OFF OFF OFF Node Address set to 64
4.14.3 Protocol & Supported Functions
Devices on a Modbus Plus network have two ways of exchanging data. One is through fast
cyclic I/O data called Global Data, and one through a somewhat slower Modbus protocol for
point-to-point parameter data transfer. The 105G supports both Global Data and point-to-point
data; however the module cannot initiate point-to-point commands but only respond to and
accept point-to-point commands initiated by other nodes on the network.
Modbus Plus is a token bus network. This means that each device on the network will receive the
token on a cyclic basis. When a device on the network receives the token it is able to broadcast
up to 32 words of Global Data. All other devices on the network will ‘see’ this data, and
depending on their configuration have the option to use some, or all, of the broadcast data.
Consequently, the 105G Modbus Plus module supports up to 32 words of Global Outputs (i.e.
Data To Network) and up to 32 words of Global Inputs (i.e. Data From Network).
The 105G also supports point-to-point data; however the module cannot initiate point-to-point
commands but only respond to and accept point-to-point commands. The 105G Modbus Plus
supports only the following point-to-point operations on Modbus 40000 (4X) registers:
- (0x03) Read holding Registers
- (0x06) Preset Single Register
- (0x10) Preset multiple Registers
The 105G Modbus Plus supports the following exception responses: