Re: 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>]

Only big endian order (ABCD) or little endian (DCBA) but no mixed endian (CDBA
or BACD).


On Thu, 2026-01-08 at 20:09 +0800, 高振华 wrote:
> Hi Dirk,
> Could "%#.4R" convert the 4-byte value 40 49 99 9A (in hexadecimal, big-endian order, ABCD order) corresponding to 3.15 into 99 9A 40 49 (in CDAB order)?
> 
> Thanks,
> 
> Gao Zhenhua
> 
> > -----原始邮件-----
> > 发件人: "Zimoch, Dirk" <dirk.zimoch at psi.ch>
> > 发送时间:2026-01-08 16:33:27 (星期四)
> > 收件人: "gaozh at ihep.ac.cn" <gaozh at ihep.ac.cn>, "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
> > 主题: Re: The problem of converting floating-point numbers to 4-byte format (in CDAB order) under StreamDevice
> > 
> > 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!eQZ-R8PHyYm1v6bxt6-dkwcOhSq6hFA0xrVo9m-OUXD8wd_6zt0IEWHiuhyUR9YeiW8a-z6p1V0PNvlT30JqNdwpGw$ 
> > 
> > BTW: The Modbus checksum is "%<modbus>".
> > https://urldefense.us/v3/__https://paulscherrerinstitute.github.io/StreamDevice/formats.html*chksum__;Iw!!G_uCfscf7eWS!eQZ-R8PHyYm1v6bxt6-dkwcOhSq6hFA0xrVo9m-OUXD8wd_6zt0IEWHiuhyUR9YeiW8a-z6p1V0PNvlT30JDfk-0lA$ 
> > 
> > 
> > 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
> > > 
> > > 
> 
> ------------------------------
>       
> 祝好！
> 高振华
> 
> 电话：010-88235426
> Email:gaozh at ihep.ac.cn
>