Question

Hi, 

I´m trying to convert RUT955 GPS variables using modbus as described in the https://wiki.teltonika.lt/view/Monitoring_via_Modbus guide. 

I get two decimal values using modbus read   -p 502 192.168.1.1 %MW143 2 but I´m unable to convert these values into a latitude xx.xxxx value.

Any help on this matter would be appreciate it, thanks in advance,

Answer 1

I found the solution to this, hope it may be useful to someone else.

The architecture of this number format is the following:

S	E	F
0	1_______8	9_______________________31

S: sign
E: exponent
F: faction (also referred to as the mantissa or significand)

calculation would be = (-1)^S * 2^(E [dec format]-127) * (1.F)[Base 10]

Take the reading of RTU995 as an example. If the frequency reading in floating point registers are (read -p 502 192.168.1.1 %MW143):

1020: 0100001001000111
1021: 0000000000000000

Combine 2 registers in binary format to become:
01000010010001110000000000000000

According to the IEEE Floating Point Standard, split the combined value according to the structure:
 

S	E	F
0	10000100	10001110000000000000000

When S=0, it is a positive number (i.e. S=1 means the value is negative).
The value in E is 10000100, which is 132 in decimal.
The remaining portion is placed in F, which is 0.10001110000000000000000 (Base 2).
1.F is 1.10001110000000000000000 in base 2, which equals to 1.55468750000000000000000 in Base 101.554687500000000000000001.55468750000000000000000
Placing this in the formula results in (-1)^(0) * 2^(132-127) * (1.55468750000000000000000) = 49.75