Ecat[i].Io[j].Data storage ± 10v data

[zerbzhang]

For an analog quantity of ± 10v, the ecat slave station data ranges from negative 32768 to positive 32767; When reading data on Pmac_ECAT, the Ecat [i]. io [j]. Data data is 0-65535；

How to Set Up to Display Correct Results Consistent with ECAT Slaves？

[Gregs]

It appears that the ESI file is giving wrong info.  That said, a PLC might be used to write the value into Sys.UData[x] and read it out of Sys.IData[x].

[zerbzhang]

8 hours ago, Gregs said:

It appears that the ESI file is giving wrong info.  That said, a PLC might be used to write the value into Sys.UData[x] and read it out of Sys.IData[x].

 I am currently using the WAGO 750-476 module.   

Ecat [i].io [j].data is stored in Sys.IData[x], Sys.UData[x]. I want to know,

1）How does Sys.UData[x] correspond to the Ecat IO address？

2）Sys.IData[x]= Formula * Sys.UData[x]. How to set?

[leandro.martins]

2)
I vaguely know how Sys.IData[x]/Sys.UData[x] works.

Both of the elements points to the same memory address, being just interpreted in different format depending on what element you consult.

Negative values are stored in two's complement, so for converting you'll need to invert all of bits of the integer, then add 1.
When you query for Sys.Udata[x], the bits in that address would be interpreted as an unsigned integer:
bit0*2^0 + bit1*2^1+bit2*2^2...+bit31*2^31

e.g.
 

Sys.IData[0]=1

Sys.IData[1]=-1

Then

Sys.UHex[0]=$1
Sys.UData[0]=1

Sys.UHex[1] = $ffffffff // Inverting $00000001 --> $fffffffe, then add 1 --> $ffffffff
Sys.UData[1] = 4294967294

I don't know if that was exactly the question, but I hope that helps.
I'm sure that Gregs can complement my answer if necessary.

Edited August 21, 2023 by leandro.martins

[Gregs]

What should be done depends on what's happening.  

Analog Voltage	PMAC Reading (Shift by 32k)	PMAC Reading (Read as Signed)
-10V	0	32768
-5V	16384	49152
0V	32768	0
5V	49152	16384
10V	65536	32767

It's possible that PMAC is reading the correct data, but then just shifting it by 32384, and in that case, subtract and scale.  A PLC like this could be used:

    GLOBAL AnalogIn
    OPEN PLC AnalogReadPLC
    AnalogIn = (SensorValue - 32768)/3276.8  // divide by 3276.8 to convert to volts
    CLOSE

It's also possible that the data is signed, but the ESI file is telling PMAC to read it as unsigned, so the fix is to read it as signed.  In that case, writing it into UData, then reading it out of Idata may fix it.  To do that one, you'd need a PLC like:

    GLOBAL AnalogIn
    OPEN PLC AnalogReadPLC
    Sys.Udata[10] = SensorValue
    AnalogIn = Sys.Idata[10]/3276.8
    CLOSE

So, from just "it's showing 0-65k", that's not enough info to determine how to fix it. We'd need  to know when it shows 0, and when it shows 65k.

[Alex Anikstein]

Just to add on a tiny bit, to explain the table Greg shared but in picture form...

 

If the data PMAC is receiving is simply shifted, such that 0V corresponds with an ECAT[i].IO[j].Data value of 32k, then the data would look like this:

However, it is also possible that the data is coming across in the incorrect data type--the device is sending signed data, but PMAC is reading it as unsigned data. In that case, 0V would correspond with ECAT[i].IO[j].Data having a value of 0, and it would "track" up to the value of 32767. However, what PMAC interprets as the most significant bit would actually be a sign bit, so any negative value sent by the device, PMAC would interpret as 32768 or greater. In this case, the data would look like this:

To correct this case, you would have to compensate for the incorrect ESI file provided by the manufacturer and "trick" PMAC to reading the data as being signed. The easiest way to do this is to make use of Sys.nData[x] (such as .IData or .Udata in this case) to read the data as a different type than what PMAC originally believed.

[zerbzhang]

thanks，Alex

[Gregs]

Thanks Alex.

One more thought, another approach could be to process the value as an entry in the encoder conversion table, for example with settings like this:

     Sys.Udata[]=32768

     EncTable[].pEnc=Ecat [i]. io [j]. Data

     EncTable[].pEnc1=Sys.Udata[]

     EncTable[].type=9