UART Communication Settings/en

Registers of parameters of data exchange via RS-485

In the factory configuration, all Wiren Board devices are supplied with the following RS-485 settings: 9600 bps, no parity bit (none), stop bit count — 2. However, the firmware of almost all modern Wiren Board devices supports additional registers, which set parameters of data exchange via RS-485:

Register / address	Type	Read/write	Value by default	Format	Function
110	holding	RW	96	baud rate / 100	RS-485 port speed, divided by 100. Permissible speeds: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
111	holding	RW	0		set the parity bit of the RS-485 port. Valid values: 0 - no parity bit (none), 1 - odd , 2 - even
112	holding	RW	2		umber of stop bits of RS-485 port. Valid values: 1, 2

Changing data exchange settings

To be able to access the device that supports the modbus RTU Protocol over the RS-485 bus, it is necessary to know its modbus address, as well as the data exchange rate, parity, the number of stop bits installed on the device. Important: Before executing the commands below, stop the wb-mqtt-serial: service wb-mqtt-serial stop service

You can find out the current settings of the data exchange parameters by reading the value of the above registers, for example:

   (echo -n '100 \* '; echo  -e `modbus_client --debug -mrtu -b9600 -pnone -s2 /dev/ttyAPP1 -a0x01 -t0x03 -r110 | grep Data | sed -e 's/Data://' -e 's/s//g'` | xargs printf "%d") | xargs expr

   9600

For details, see the description of the modbus_client command. Important: the examples below use the /dev/ttyAPP1 port. If the device is connected to another port, you must replace /dev/ttyAPP1 with the name of that port!

You can write a new value by using the following command:

   modbus_client --debug -mrtu -b9600 -pnone -s2 /dev/ttyAPP1 -a0x01 -t0x06 -r110 1152

The device now transmits and receives data at 115200 bps.

Writing to the appropriate registers changes the parity and the number of stop bits.

In this case, a paradoxical situation arises: we can not know the value of the speed, if we do not specify its value in advance when referring to the device! Therefore, you should pay attention to what communication parameters you set. Stick a sticker with the new settings on the device. If all communication parameters are unknown, you can find them only by searching:

   #/bin/bash
   for l in {1,2};
   do
   for k in {none,odd,even};
   do
       for j in {1200,2400,4800,9600,19200,38400,57600,115200}; 
       do
           for i in {1..247}; do 
                       modbus_client -mrtu /dev/ttyAPP1 --debug -o 300 -a$i -t3 -r0x80 -b$j -s$l -p$k 
           done 2>/dev/null | grep Data: | sed -e 's/ //g' -e 's/\n//' | xargs -I {} printf "Speed:$j\tStop bits:$l\tParity:$k\tModbus address:{}" | grep Data: | sed -e 's/Data://'
       done
   done
   done

In this script we refer to the 0x80 register, which stores the modbus address in all Wiren Board Modbus devices. The output of the script will contain lines like these:

Speed:9600      Stop bits:1     Parity:none     Modbus address:0x0001
Speed:9600      Stop bits:2     Parity:none     Modbus address:0x0001

For stop bits, you will likely get two values: 1 and 2. You can refine the setting by reading the value from the register 112 with the already known address, speed, parity:

modbus_client --debug -mrtu -b9600 -pnone -s2 /dev/ttyAPP1 -a0x01 -t0x03 -r112

or

modbus_client --debug -mrtu -b9600 -pnone -s1 /dev/ttyAPP1 -a0x01 -t0x03 -r112

   SUCCESS: read 1 of elements:
   Data: 0x0002

If you receive an error while reading from register 112, the device does not support setting communication parameters. In this case,the default value of 2 stop bits is used for communication.