Toshiba T300MVi - Manual (Page 52)

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15. Protocol-Specific Information
This section will discuss topics that are specific to each of the available network
selections.
15.1 Modbus
The interface supports Modbus slave functionality via both Modbus RTU and
Modbus TCP/IP, and Modbus master functionality via Modbus RTU. The slave
implementations share common access methods, which is to say they support
the same functions and reference the internal points via a common “Modbus
Slave” holding register assignment. Other notes of interest are:
•
Points are addressed by their assigned holding register (4X reference) via
Modbus slave protocols.
•
Points can access both holding register (4X references) and input registers
(3X references) via Modbus master protocols.
•
Supported Modbus slave functions are indicated in Table 2.
Table 2: Supported Modbus Slave Functions
Function Code Function
Modbus TCP/IP
Class
1 Read coils 1
3 Read multiple registers 0
5 Write coil 1
6 Write single register 1
15 Force multiple coils 2
16 Write multiple registers 0
•
Register number entry radix is decimal (e.g. 10 = 10
10
)
•
Configuration tip: Improved network utilization may be obtained by
appropriately grouping points into blocks having contiguous holding
register assignments. In this way, the “read multiple registers” and “write
multiple registers” functions can be used to perform transfers of larger
blocks of registers using fewer Modbus transactions compared to a
situation where the read/write registers were arranged in an alternating or
scattered fashion.