31.07.2020, 07:33
The first number before the address is function number: 1= coil, 3 = holding register, 4 = input register. The actual address might be in hex but you will have to check. You probably will have to subtract 1 from the address. Try reading register 0 or 1, it should contain the alarm status. But as Daniel said once you get addressing right using profile is more convenient.