Experimental Physics and
Industrial Control System

From: Jemian, Pete R. <jemian at anl.gov>
Sent: Thursday, October 19, 2023 7:53 PM
To: Pearson, Matthew <pearsonmr at ornl.gov>; tech-talk at aps.anl.gov
Subject: [EXTERNAL] Re: 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