iSMA-B-MG-IP User Manual
www.ismacontrolli.com
DMP260en | 1st Issue rev. 6 | 05/2022
page 12 of 29
5 Modbus Gateway
Figure 6. iSMA-B-MG-IP as a Modbus gateway
The device simultaneously supports up to
4 Modbus TCP clients
. If the fifth device is to
be
connected
to the device, a TCP connection will be rejected. In order to secure the
device before filling up the call list, a mechanism for monitoring each Modbus TCP
connection was introduced. There is a parameter called
Modbus TCP Connection
Timeout
(by default, 60 s); if there is no request from the Modbus TCP client during this
time, the device will close the connection.
To read internal registers of the device, it needs to generate the correct Modbus TCP
frame with address according to the setting of a DIP switch. If the address is different, the
frame will be sent to the COM1 port.
If the device receives an incorrect Modbus TCP frame, it sends back a frame with an error
code:
0x01 - if the function code in the query is not supported;
0x02 - if the address of the register is invalid;
0x03 - if the amount of data disagrees in the query.
If the query is correct, the device instantly generates answer with data or
acknowledgment of receipt of data, depending on the query.