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PCS100 UPS-I User Manual
12.3 Modbus TCP
Modbus TCP connection is provided with PCS100 UPS-Is fitted with the GDM user interface. Connection is via an
Ethernet cable to the Ethernet port on the bottom of the GDM. Read Only access is available to the parameters in
Table 12-2: PCS100 UPS-I Modbus TCP user parameters
Modbus protocol is an open messaging structure developed by Modicon in 1979, used to establish master-slave
(client/server) communication between intelligent devices. It is a de facto standard, truly open and the most
widely used network protocol in the industrial manufacturing environment.
Modbus TCP specification (available from www.modbus-ida.org/specs.php) was developed in 1999, combining
the physical network (Ethernet) with a networking standard (TCP/IP) and a vendor neutral data representation
(Modbus) giving an open, accessible network for exchange of process data.
Modbus TCP basically embeds a Modbus frame into a TCP/IP frame in a simple manner.
12.3.2
Supported Functions
The following Modbus functions are supported:
Function 3 – Read multiple registers
Function 4 – Read input registers
Function 8 – Diagnostic request
The Modbus server has the following characteristics:
Maximum registers per request
Maximum TCP connections
Modbus server port
Refer to section 10 for network configuration details. There are no additional Modbus TCP specific user
parameters.
12.3.3
Performance
Each user parameter read for registers in Table 12-2 can take up to 300 ms due to the latency of the PCS100
internal communication bus. To improve Modbus client responsiveness (such as for use in SCADA systems), the
Modbus TCP server caches a range of user parameters as specified in Table 12-3).
The Modbus TCP server responds to reads from the cached addresses in typically less than 3 milliseconds.
However the latency in a parameter changing value (the time it takes for the cached values to be refreshed) is
typically around 3 seconds.
12.3.4
Modbus TCP User Parameters
The following table lists the user parameters available from the PCS100 UPS-I.
The address listed is the offset (raw) address. For 4xxxx address add 40001 to the offset address. Each address
refers to a 16 bit register.
16
5
502
119
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