Modbus

SmartPi 3.0 Modbus TCP and Modbus RTU settings

From software version 1.0.0 -3.0.0 (from June 2019), the SmartPi has the option of being read out via Modbus RTU (only SmartPi 3.1) and Modbus TCP (slave).

With Modbus TCP, communication takes place via the network interface.
With Modbus RTU the communication takes place via the RS485 interface of the SmartPi.

Currently, the Modbus settings must still be made manually in the configurationsfile /etc/smartpi.

Own installation vs ready image

We recommend to use our ready-made image when using Modbus RTU,

because for a smooth operation some settings have to be done at the serial ports of the Raspberry Pi.

If you have your own image, please proceed as follows:
Please log in to the SmartPi via SSH.

sudo nano /boot/cmdline.txt

there remove console=/dev/serial1 and console=serial0,115200

save CTRL+O and close CTRL+C

sudo nano /boot/config.txt

at the end insert the two lines

dtoverlay=pi3-miniuart-bt
enable_uart=1
core_freq=250

save CTRL+O and close CTRL+C

sync
sudo reboot

Now you can use the RS485 bus via /dev/serial0.

Modbus RTU (only SmartPi 3.1)

Connect the SmartPi via the RS485 terminals A and B to the Modbus master you are using. Please make sure that the polarity of the terminals A and B is correct. If A and B are reversed, no communication can take place.

The terminating resistor can be activated and deactivated via the jumper. If the SmartPi is at the beginning or at the end of the RS485 bus or if only master and slave are connected, the jumper must be set. If the SmartPi is in the middle of the bus, the jumper should be pulled out.

Konfiguration

You can set the Modbus configuration via the configuration file /etc/smartpi.

[modbus]
modbus_rtu_enabled=0
modbus_tcp_enabled=0
modbus_rtu_address=1
modbus_rtu_device_id="/dev/serial0"
modbus_tcp_address=":502"

If the entry does not exist in the configuration file, you can simply create the entry at the end of the file.
To enable Modbus RTU, set the value of modbus_rtu_enabled to 1. With the help of the value modbus_rtu_address you can set the SlaveID. A SlaveID may only occur once in a bus. For example, if you operate several SmartPi on one Modbus, change the SlaveIDs accordingly. The value modbus_rtu_device_id can be used to select the corresponding serial interface. This value actually does not have to be changed.

RS485-Anschluss für Modbus RTU — Image 1: RS485 connection for Modbus RTU

Modbus TCP

With Modbus TCP the communication takes place via the network interface (LAN or WLAN) in the network.
Also for Modbus TCP you find the settings in the configuration file /etc/smartpi.

[modbus] modbus_rtu_enabled=0 modbus_tcp_enabled=0 modbus_rtu_address=1 modbus_rtu_device_id="/dev/serial0" modbus_tcp_address=":502"

If the entry does not exist in the configuration file, you can simply create the entry at the end of the file. To enable Modbus TCP, set the modbus_tcp_enabled value to 1. The only other parameter is modbus_tcp_address. This value can be used to set the IP address and port that the SmartPi listens on. Default is that on all IP addresses of the SmartPi on port 502 is listened.

Modbus Register

Datatyp: IEEE-754 Floating Point

Register	Value
0	I1	MSB
1		LSB
2	I2	MSB
3		LSB
4	I3	MSB
5		LSB
6	I4	MSB
7		LSB
8	U1	MSB
9		LSB
10	U2	MSB
11		LSB
12	U3	MSB
13		LSB
14	P1	MSB
15		LSB
16	P2	MSB
17		LSB
18	P3	MSB
19		LSB
20	CosPhi 1	MSB
21		LSB
22	CosPhi 2	MSB
23		LSB
24	CosPhi 3	MSB
25		LSB
26	F1	MSB
27		LSB
28	F2	MSB
29		LSB
30	F3	MSB
31		LSB
32	Balanced	MSB
33		LSB