restmbmaster is a simple daemon that allows user to access Modbus slaves over Rest API. The slaves could be either connected over serial line (Modbus RTU protocol), or over TCP (Modbus TCP protocol).
To run connecting to Modbus TCP:
$ restmbmaster -c tcp://test.abc:1000 -p 8080
To run connecting to Modbus RTU:
$ restmbmaster -c rtu:/dev/ttyS0?baud=9600 -p 8080
To run according to the configuration from file:
$ restmbmaster -f myconfig.conf
When restmbmaster is running, one can use for example curl to communicate with Modbus slaves. In the following example, slave with address 55 is queried for the value of input register with address 10:
$ curl http://127.0.0.1:8080/slaves/55/input-registers/10
34
It is possible to query multiple registers (in sequence) at once:
$ curl http://127.0.0.1:8080/slaves/55/input-registers/10?count=4
34 78 234 2
To write new value (434) to holding register 20 the "PUT" method has to be used:
$ curl http://127.0.0.1:8080/slaves/55/holding-registers/20 -d "434" -H "Content-Type: text/plain" -X PUT
It is also possible to write to a sequence of registers (20-26):
$ curl http://127.0.0.1:8080/slaves/55/holding-registers/20 -d "434 48 32 92 1 0 3" -H "Content-Type: text/plain" -X PUT
restmbmaster is prepared to be run in multiple parallel instances to allow to access multiple buses. One just have to prepare a configuration file for each bus and ask systemd to spawn the instance.
$ sudo mkdir /etc/restmbmaster/
$ sudo cp /usr/share/doc/restmbmaster/example_configs/sample_tcp.conf /etc/restmbmaster/mytcpmodbus1.conf
$ sudo systemctl start restmbmaster@mytcpmodbus1
$ sudo systemctl status restmbmaster@mytcpmodbus1
● restmbmaster@mytcpmodbus1.service - Rest API Modbus master mytcpmodbus1
Loaded: loaded (/usr/lib/systemd/system/restmbmaster@.service; static; vendor preset: disabled)
Active: active (running) since Sat 2019-12-28 18:36:54 CET; 1s ago
Main PID: 8337 (restmbmaster)
Tasks: 1 (limit: 4915)
Memory: 588.0K
CGroup: /system.slice/system-restmbmaster.slice/restmbmaster@mytcpmodbus1.service
└─8337 /usr/bin/restmbmaster -f /etc/restmbmaster/mytcpmodbus1.conf
Dec 28 18:36:54 nanopsycho systemd[1]: Started Rest API Modbus master mytcpmodbus1.