Internet PLC Forum

I tried the program from tech support however it only showed a value of 20 in DM[1] which I guess meant 20 characters. Then I tried Gary's and all I got was numbers in DM[1] so something is wrong in both programs.
This is what I need A$ holds a maximum of 20 characters example: A$ = "OPEN EMERG STOP SW  " so if I am correct it would fill 10 consecutive DM's
so on simulation I should see values in DM[1] to DM[10] if there are two BYTES stored in each DM 

Lorne,

I pass strings back and forth between Weintek HMIs and TRI PLCs.  Weintek uses arrays of integers to store strings and packs 2 8-bit characters in each 16 bit value. 

This is the code that I use to convert a PLC string variable into an array of registers that can be accessed via Modbus. The HMI reads/writes 16 sequential registers in the PLC to read/write string data. I picked an array size of 16 16-bit integers. This will support strings up to 32 characters.

' Copy Installation Name String from a$ to DM[] so that it can be accessed by the
'   Weintek HMI as an array of 16-bit Modbus registers
'
n = InstallationName    ' starting word in DM[] to build the data for the HMI

' SizeInWords is defined as 16.  16 sequential DM[] locations.
'
for i = 1 to SizeInWords step 2

    ' Two 8-bit ASCII characters are packed into each 16-bit DM value
    '
    ' The Weintek HMI expects strings to be packed into sequential 16-bit words.
    ' The first character in a string is in the LSB of the first word
    '   The second character will be in the MSB of the frist word.
    '
    ' The rest of the bytes are filled with 0x00. This keeps the HMI string object
    '   sane.
    '
    ' Please note that asc() is spec'd to return 0x00 when index is beyond
    '   the end of the string, A$.  It seems to do this in test. This
    '   usage ensures that the entire DM[] array is 0 filled beyond the end
    '   of the string characters.
    '
    DM[n] = asc(A$,i+1) * 256
    DM[n] = DM[n] + asc(A$,i)
    n = n + 1           ' next word in DM[]
next


Gary Dickinson

I have a third party device connected to a FX series PLC that uses the MODBUS RTU protical. The developer knows how to read the values of the Inputs, Outputs, Internal Relays as well as the DM values. However is there any way they can read what is stored in say A$?
The A$ will show a 20 character text message such as A$ = "OPEN EMERGENCY STOP " Can anyone tell me how they can read the contents of the A$ using MODBUS RTU commands?

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Hi
   Thank you support and Gary for looking into this for me. Just before I got this reply I had tried the setsystem 16,1  and yes it made no difference. So as it stands I will keep the remote input data at inputs 81 onwards which seems to work fine.
Regards Peter