IDEC FC6A-C16K1CE Communications Manual page 152

6: M C
ODBUS OMMUNICATION
Modbus TCP Server Communication Settings
Local Host Port No.
Configure the local host port number between 0 and 65,535. The same local host port number can be used with multiple
connection numbers.
If the same port number is used with multiple connections, Modbus TCP clients (as many as the number of the connections) can
communicate with FC6A Series MicroSmart through the same port number.
Allow Access by IP Address
You can set the IP address for a device to permit access. By setting the allowed IP address, only the device with the specified IP
address can establish a connection with the FC6A Series MicroSmart and communicate with the Modbus TCP server. When the
same local host port number is configured in multiple connections, all the allowed IP address settings are effective. If a connection
in which the allowed IP address it not configured uses the same local host port number, arbitrary access is allowed through the
port.
Example 1) If two connections use the same local port number and an allowed IP address is not configured for both
connections, access from a total of two clients with any IP addresses is accepted.
Example 2) If two connections use the same local port number and 192.168.1.101 and 192.168.1.102 are configured as the
allowed IP addresses, access from a total of two clients whose IP addresses are 192.168.1.101 and 192.168.1.102
is accepted.
Example 3) If connection 1 and 2 use the same local port number, an allowed IP address 192.168.1.101 is configured for
connection 1, and the allowed IP address is not configured for connections, access from a total of two clients with
any IP addresses is accepted.
Modbus TCP Communication Format
This section describes the communication format used for Modbus TCP client and server communication. Modbus TCP
communication format starts with the Modbus TCP header followed by the RTU mode communication format without the idle 3.5
characters at both ends and CRC as shown below.
Modbus TCP Communication Format
Transaction ID Protocol ID
2 bytes 2 bytes
Modbus TCP Header
RTU Mode
Communication Format
Transaction ID
The Modbus TCP server (slave) returns the request ID sent from the client (master) without any change. When receiving the
returned request ID, the client can confirm to which request the response was returned. When confirmation is not required,
designate 0 as a transaction ID.
Protocol ID
Designate 0 to identify Modbus TCP protocol.
Message Length
Designate the length of the following message in bytes.
Unit ID
The ID for identifying the device. Store the slave number of the Modbus TCP server. The FC6A Series MicroSmart Modbus TCP
server accepts and processes requests when the unit ID of the received request is not 0. When the unit ID is 0, the received
request is processed as broadcast communication and no response is returned to the Modbus TCP client.
Function Code
Designate a function code, such as 01 (read coil status) and 02 (read input status).
Data
Designate required data for each function.
6-26
Message Length
Unit ID
(bytes)
2 bytes 1 byte
Slave No.
Idle
3.5 characters
1 byte
FC6A S M S A
ERIES ICRO MART
Function
Data
Code
1 byte N bytes
Function
Data
Code
1 byte N bytes
- -O T C
LL IN NE YPE OMMUNICATION
CRC
Idle
3.5 characters
2 bytes
M FC9Y-B1730
ANUAL