Event-based program to control Modbus Air-Conditioner from KNX

Example: Event-based program to control Modbus Air-Conditioner from KNX

Task

When KNX group address receives 1, write TRUE in according Modbus register, if 0 – then FALSE.

Event-based program

• Assume we have already added object 1/1/1 (1bit)
• In Scripting ->Event-based add a script assigned with group address 1/1/1

• Add the following script in Scripting Editor for this program

Source code

require('luamodbus')
mb = luamodbus.rtu()
 
mb:open('/dev/ttyS2', 9600, 'E', 8, 1, 'H')
mb:connect()
 
mb:setslave(1)
 
-- compare either 1/1/1 received 1 or 0
if event.datahex == '01' then
   -- write in specific Modbus register TRUE if 1/1/1 is 1
   mb:writeregisters(0x9C40, 0x11)
else
   -- write in specific Modbus register FALSE if 1/1/1 is 0
   mb:writeregisters(0x9C40, 0)
end

Encoded A/C values

Some Air Conditioners are keeping enocded values in registers, you need to encode them first from HEX to use in the further scripts.
For example, value = 0x0cba after executing the below commands will give 24.2

Source code

hex = lmcore.inttohex(value, 2)
temp = knxdatatype.decode(hex, dt.float16)

How to encode KNX temperature into 16 Hexadecimal data and write to Modbus registers:

Source code

function encodetemp(value)
   local hex = knxdatatype.encode(value, dt.float16).datahex
   return tonumber(hex, 16)
end
 
value = 20.8
mb:writeregisters(30001, encodetemp(value))