Re: modbus reading arrays of floats

["Jemian, Pete R. via Tech-talk" <tech-talk@aps.anl.gov>]

ULONG?

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From: Tech-talk <tech-talk-bounces@aps.anl.gov> on behalf of Pearson, Matthew via Tech-talk <tech-talk@aps.anl.gov>
Sent: Thursday, October 19, 2023 5:12:39 PM
To: tech-talk@aps.anl.gov <tech-talk@aps.anl.gov>
Subject: modbus reading arrays of floats

 

Hi,

 

I have a device which supports reading arrays of floats (IEEE Float32) over Modbus/TCP.

 

Am I right in thinking that currently this isn’t supported by the Asyn modbus support? It seems to support arrays of ints, but not floats.

 

Interestingly, this almost works:

 

record(waveform, "$(P)$(R)TCA") {

  field(FTVL,  "ULONG")

  field(DTYP,  "asynInt32ArrayIn")

  field(INP,   "@asyn($(PORT)8w4,2064,1)FLOAT32_LE")

  ….

}

 

By specifying the datatype to be FLOAT32_LE, the modbus driver correctly converts the byte data to floats, but the waveform only gives me the integer part of the number.

 

So as a work-around I’ve implement multiple reads, one per Float32. This works fine, and I’ll likely stick with it.  

 

However, is there a smarter workaround? For example, can I read the data as a block of Ints, then convert to IEEE Float32 in the database (without writing a subroutine)?

 

Cheers,

Matt