Modbus MQTT 2 Register Formats

RouterOS Scripting
1

Hi have a modbus device that uses 32bit signed big-endian formatted number
So in the script using
:local modbusread [/iot modbus read-holding-registers slave-id=1 num-regs=2 reg-addr=514 as-value once];

This gives the result as 15,3492 so how can this be formatted to give the actual register value of 986532 to send to the IoT MQTT

2

The help page shows how to get the values, but the “($output->“values”)” is hidden unless you scroll:

[admin@device] > {:local output [/iot modbus read-holding-registers slave-id=0x03 num-regs=0x1 reg-addr=0x0 as-value once];:put [($output->"values")]}
2349
[admin@device] > {:local output [/iot modbus read-holding-registers slave-id=0x03 num-regs=0x5 reg-addr=0x0 as-value once];:put [($output->"values")]}
2353;3;500;75;38

In the 2nd example, it’s an array type. So you may need to use a :foreach on the results of the “/iot read-holding-registers”

3



To be more specific, each member of the array I think is 16-bit. So you can multiple the first element (15) * 65536, the add the 2nd 16-bits (3492) to that.

So 15*65536+3492 = 986532, which is what you’re expecting.

I don’t have a KNOT, but this should be pretty close:

{
:local modbusread [/iot modbus read-holding-registers slave-id=1 num-regs=2 reg-addr=514 as-value once];
:local reg514 ( ( ($modbusread->"values"->0) * 65536 ) + ($modbusread->"values"->1) )
:put $reg514
}
4

Thank for the detail, yes that was result we are looking for. Appreciated your input.