Re: The problem of converting floating-point numbers to 4-byte format (in CDAB order) under StreamDevice

["Zimoch, Dirk via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Gao

As Mark already wrote, better use the dedicated Modbus driver, but for
completeness here is the answer: Use format "%.4R"

%R is the "floating point raw" format and can be used with precision .4 or .8
for float or double. By default it used big endian byte order but if needed that
can be changed to little endian with "%#.4R".
https://urldefense.us/v3/__https://paulscherrerinstitute.github.io/StreamDevice/formats.html*rawdouble__;Iw!!G_uCfscf7eWS!YPu7MZfgs8VAOm3wAtNSUfcy2Lr84r4_MbjAcI9J-ZBg0-qnnB1btmrlWdWX89n1qdeVmjWHYI1dThGj46br-EOfcQ$ 

BTW: The Modbus checksum is "%<modbus>".
https://urldefense.us/v3/__https://paulscherrerinstitute.github.io/StreamDevice/formats.html*chksum__;Iw!!G_uCfscf7eWS!YPu7MZfgs8VAOm3wAtNSUfcy2Lr84r4_MbjAcI9J-ZBg0-qnnB1btmrlWdWX89n1qdeVmjWHYI1dThGj46Z9g3_EMg$ 


Dirk

On Wed, 2026-01-07 at 17:53 +0800, 高振华 via Tech-talk wrote:
> 
> Hi all,
> 
> 
> 
> I am conducting Modbus RTU communication with a device and need to convert a 32-bit floating-point number into 4 bytes of hexadecimal data and then send it to the device.
> 
> For example: 3.15 converted to 4 bytes is 40 49 99 9A (in hexadecimal, big-endian order, ABCD order).
> 
> Using StreamDevice, how should I convert to the CDAB order? (For example, the CDAB order corresponding to 3.15 is 99 9A 40 49).
> 
> Does StreamDevice have a corresponding conversion symbol?
> 
> 
> 
> 
> Best regards，
> 
> 
> Gao Zhenhua
> 
> 
> BSRF
> 
> Email:gaozh at ihep.ac.cn
> 
>