Modbus Slave- commands 3 and 16

[mmotte]

Last year I was doing some research and i wanted to record the Temperature and humidity (DHT22) in 22 compartments. This was in a factory with lots of steel and concrete and noise spread over a 500 ft radius. Wifi didn't look real feasible. So I opted for a wired network, RS485 and modbus protocol. There are modbus simulators that you can check the slave with from a PC. http://www.modbustools.com/modbus_poll.html . I actually used php to write a program to gather the data into a MySQL database every 5 minutes. Never got implemented yet at the factory but I do have 7 stations running full time at home . Don't get bothered by the BME280 stuff, i am just recording some data and this demonstrates how to add data to the outbuffer.

' Modbus RTU Slave
' Only two commands  3  read reg and 16 mod reg
' command 3  reads from the variable array "outbuffer(20)" which is ram with sensor data plugged in
'command 16 writes to RAM  and is going to be used for limits
'Adopted/severely modified from Andrzej Sokulski,
' andrzej@modbus.pl - www.modbus.pl
' All rights reserved.
'Rewritten by Mike otte  December 2016/2017
' All rights reserved.
' This software is free you can redistribute it and/or
'  modify it under the terms of the GNU Lesser General Public
'  License as published by the Free Software Foundation; either
'  version 2.1 of the License, or (at your option) any later version.
'*
'  This software is distributed in the hope that it will be useful,
'
'  but WITHOUT ANY WARRANTY;
'  In no event shall the regents or co ntributors be liable for any direct,
'  indirect, incidential, special, exemplary, or consequential damages.
'Modbus slave based on PIC 16F886 PIC16F1705
'This slave supports modbus function 3 (read holding registers) and 16 (preset multiple registers)
' command 3  reads from the variable array "outbuffer(20)" which is ram
'command 16 writes to EEPROM  and is going to be used for limits
'The RS232 is set to baudrate - 9600, data bits - 8, stop bits 1, parity - none
'The hardware USART and MSSP/I2C are defined below
'The Timer 2 is used for detecting end of modbus frame

'Master  Query
'read registers 40000–40008 from slave device 17:
'Example   = $0A$03$00$00$00$08$45$77
'Field Name         (Hex)
'Slave Address        $0A
'Function             $03
'Starting Address Hi  $00
'Starting Address Lo  $00
'No. of Points Hi     $00
'No. of Points Lo     $08
'Error Check ( CRC)   $45 ––  16bits = last two bytes of packet
'                     $77

'Slave RESPONSE
'0A 03 10 01 83 00 D1 00 05 67 C0 00 08 04 F0 84 1B EF DF 13 3E
'Example                ASCII       RTU
'Field    Name  (Hex)   Characters  8–Bit Field
'Header  :              (colon)   None
'Slave Address    $0A   0 A       0000 1010
'Function         $03   0 3       0000 0011
'Byte Count       $10   1 0       0001 0000
'Data Hi          $01   0 1       0000 0001
'Data Lo          $83   8 3       1000 0011
'Data Hi          $00   0 0       0000 0000
'Data Lo          $D1   D 1       1101 0001
'.....
'Data Hi          $EF   E F       1110 1111
'Data Lo          $DF   D F       1101 1111
'Error Check      $13   1 3       0001 0011        LRC (2 chars.) CRC (16 bits)
'CRC              $3E   3 E       0011 1110
'Trailer for ascii       CR LF
'    Total Bytes: 25        11          ASCII mode takes many more chars
'This code only implements RTU!

' Preset Multiple Holding  Registers
'   ***********            Function 16   Hex $10
'
'Field Name (Hex)
'Slave Address       $10
'Function            $10
'Starting Address Hi $00
'Starting Address Lo $01
'No. of Registers Hi $00
'No. of Registers Lo $02
'Byte Count          $04
'Data Hi             $00
'Data Lo             $0A
'Data Hi             $01
'Data Lo             $02
'Error Check         $__ (LRC or CRC) –– two bytes
'                    $__
'Response from slave
'Field Name (Hex)
'Slave Address        $11
'Function             $10
'Starting Address Hi  $00
'Starting Address Lo  $01
'No. of Registers Hi  $00
'No. of Registers Lo  $02
'Error Check          $__(LRC or CRC) –– two bytes
'                     $__
; ----- Configuration

  #chip 16F1705,8
  #option explicit
  #config  WDT_OFF, LVP_OFF

   'Generated by PIC PPS Tool for Great Cow Basic
    'PPS Tool version: 0.0.5.11
    'PinManager data: v1.55
    '
    'Template comment at the start of the config file
    '
    #startup InitPPS, 85

    Sub InitPPS
        UNLOCKPPS

            'Module: EUSART
            RXPPS = 0x0005    'RA5 > RX
            RC5PPS = 0x0014    'TX > RC5
            'Module: MSSP
            RC0PPS = 0x0010    'SCL > RC0
            SSPCLKPPS = 0x0010    'RC0 > SCL (bi-directional)
            RC1PPS = 0x0011    'SDA > RC1
            SSPDATPPS = 0x0011    'RC1 > SDA (bi-directional)

        LOCKPPS
    End Sub
    'Template comment at the end of the config file

  #include <BME280.h >
  #include <DHT.h >

; ----- Define Hardware settings
  ' Define I2C settings - CHANGE PORTS if required
  #define HI2C_BAUD_RATE 400
  #define HI2C_DATA PORTC.1
  #define HI2C_CLOCK PORTC.0
  'Initialise I2C Slave
  'I2C pins need to be input for SSP module
  Dir HI2C_DATA in
  Dir HI2C_CLOCK in
 'MASTER
  HI2CMode Master

'DHT 22  Humidity and Temperature
  #DEFINE DHT_TYPE 22
  #DEFINE DHT_PIN PORTA.2
  '#define sensor  PortA.2  'PortA.0     ;RH/Temp sensor on pin
  dir PORTA.2 in          'sensor in

'InitUSART   usuart is on a RS485 network
  #define USART_BAUD_RATE 9600
  #define USART_BLOCKING
  #define MaxDir  PortA.4     'RS485 direction  Max485 chip
  dir PortA.4 Out         ' MAX485 direction control
' timer 2 determines the end of the frame
  pr2 = 0
  Inittimer2 PS2_16, 0 'Prescale 1:16 /Postscale 1:1
  Starttimer 2

  On Interrupt UsartRX1Ready Call SerialInterrupt
  On Interrupt Timer2Match Call Timer2Interrupt

;----- Variables
Dim SlaveAddress as byte
SlaveAddress = 10                 ' Modbus slave adress (1..255)

dim DHT_rh ,DHT_cels, DHT_fahr as integer
dim DHT_error  as Byte

Dim buffer(74)             'Modbus frame buffer - change if want to get more than 32 registers in single frame
Dim outbuffer(50)          ' buffer to collect data to send back before transfering to buffer
Dim ADC_P, ADC_T as Long    ' variables used by BME280_Read_TPH
Dim ADC_H as Word

Dim  mbB0     as byte            'Variables definition
Dim  mbB1     as byte             ' transmit this byte
Dim  mbW0     as word             'address pointer
Dim  MBFrame  as byte
Dim  NewFrame as byte
Dim  Length   as byte
Dim  TMR2Ticks as byte            'used to determine end of RTU frame
Dim  mbi      as byte             ' forloop index
Dim  counter1 as word             ' waste time counter to do nothing
Dim  counter2 as word             ' waste time counter to do nothing
Dim Generator as word             ' CRC variable/constant 40961
Dim Temp as word
Dim CRC as word                   ' CRC result
Dim mbj as byte                   ' forloop index
Dim mbBit as bit                  ' temp bit var

TMR2Ticks = 0
Length = 0
wait 500 ms

mainloop:

For counter2 = 0 to 5  ' The main program
For counter1 = 0 to 10000  ' Write your code here
next counter1
next counter2
  'diagnostic - used for testing
  'MaxDir = 1
  'hserprint "I am here "
  'MaxDir = 0
  ' MaxDir = 1
  'hserprint Length
  'MaxDir = 0

' Modbus protocol function
  If NewFrame = 1 Then           ' Check if new modbus frame is in buffer
    NewFrame = 0

    Gosub checkMB            ' Check the modbus Received frame
    Select Case MBFrame
        case 3
              'MaxDir = 1
              'hserprint "case 3 "
              'MaxDir = 0
              mbReadRegResponse      ' Response for function 3

        case 16
             mbwriteRegResponse     ' Response for function 16

        case else
             mbwriteBadRequest      ' Response for error
    end select

    Length = 0
  End if

Goto mainloop

Sub charout
xmty:                  ' USART send single byte
  If TXIF = 0 Then goto xmty            ' Wait for transmit register empty
  TXREG = mbB1                     ' Send character to transmit register
End Sub

Sub crc__16
'crc__16:                  ' Function to calculate CRC16 checksum
CRC = 65535                 'CRC is  word and is set to all 1's to start
Generator = 40961
For mbi = 1 To Length
    Temp = buffer(mbi)

    CRC = CRC # Temp      ''XOR ed

    For mbj = 1 To 8

        STATUS.C = 0
        Rotate CRC right  'CRC = CRC >> 1
        mbBit = STATUS.C
        If mbBit Then
           CRC = CRC # Generator  'XOR ed
        End If
     Next
Next

'crc16(2) = CRC / 256            ' CRC16 high byte
'crc16(1) = SysCalcTempX           ' CRC16 low byte
'CRC contains the CRC word  16 bit
End Sub

Sub checkMB

'checkMB:
'Check the modbus frame
  if (buffer(1) <> SlaveAddress) then     'Wrong Slave address
    MBFrame = 0
    Exit Sub
  end if

  if (buffer(2) <> 3) AND (buffer(2) <> 16) then 'Wrong Modbus function
    MBFrame = 0x81
    Exit Sub
  end if
  'hserprint "wrong"
  'if ((buffer(5)>0)OR( buffer(6) > 32)) then 'Too many registers
  '  MBFrame = 0x83
  'Exit Sub
  'end if
  'hserprint "Toomanyreg"
  if (Length > 74) then  'Too many bytes in frame
    MBFrame = 0x82
    Exit Sub
  end if
  'hserprint "len74"
  if (Length <9) then 'Frame too short
    MBFrame = 0x81
    Exit Sub
  end if

  'Check CRC
  Length = Length - 3
  crc__16

  'diagnostic CRC values(1)
  'MaxDir = 1
  'hserprint crc
  'MaxDir = 0

  if (buffer(Length+1) <> [byte]CRC) OR (buffer(Length+2) <> CRC_H) then 'Bad CRC16 checksum
    MBFrame = 0
  else
    MBFrame = buffer(2)   ' Frame OK !
  End if

End Sub

Sub mbReadRegResponse
    'readRegResponse:                ' Response for modbus function 3 (Read Holding Registers)
    'UPDATE Registers first
    ' DHT22  fills outbuffer 1-4 are written in the DHT22 sub
    readDHT( DHT_rh , DHT_cels,  DHT_fahr ,  DHT_error )
    outbuffer(1)=DHT_rh_H       ' Write data to buffer
    outbuffer(2)=DHT_rh         'Remember Holding Registers asked byt the master are 16 bit
    outbuffer(3)=DHT_cels_H     ' so that is two bytes
    outbuffer(4)=DHT_cels
    BME280_Read_TPH
    outbuffer(5)=adc_P_E       ' Write data to buffer
    outbuffer(6)=adc_P_U
    outbuffer(7)=adc_P_H
    outbuffer(8)=adc_P
    outbuffer(9)=adc_T_E       ' Write data to buffer
    outbuffer(10)=adc_T_U
    outbuffer(11)=adc_T_H
    outbuffer(12)=adc_T
    outbuffer(13)=adc_H_H
    outbuffer(14)=adc_H       ' outbuffer is 50 bytes of which we only filled 14 so far
    mbW0 = buffer(3)*255 + buffer(4)    'Starting address
    'mbW0 = mbW0 * 2
    mbW0 = mbW0 - 40000                    ' 40000 is secret MODBUS offset for holding registers
    buffer(3) = buffer(6)*2             ' buffer(6) is num of points(words) LO which is getting buffer ready for Tx
    'buffer(3) is the number of data bytes to xfer
    ' Header neads  MBaddress byte, MBcommand byte, Number of bytes to Xfer in the header
    'they are already there
    for mbB0=1 to buffer(3)
         buffer(mbB0+3) = outbuffer(mbB0)             ' Put data in buffer from ram ,leave room for header
    Next
    Length = buffer(3) + 3
    'Buffer(3) = Length
    crc__16
    buffer(Length +1) = [byte]CRC  'crc16(1)         ' Calculate the CRC16 for response frame
    buffer(Length +2) = CRC_H       'crc16(2)
    Length = Length + 4
    MaxDir = 1               'MAX485 direction control = Tx
    For mbB0 = 1 To Length            ' Send the response to Master
      mbB1 = buffer(mbB0)
      Gosub charout
    Next
    MaxDir = 0                 'MAX485 direction control + Rx
End sub

Sub mbwriteRegResponse
'writeRegResponse             ' Response for modbus 16 function (Preset Multiple Registers)
''Slave Address       $0A     'buffer(1)
'Function            $10      'buffer(2)
'Starting Address Hi $00      'buffer(3)
'Starting Address Lo $01      'buffer(4)
'No. of Registers Hi $00      'buffer(5)
'No. of Registers Lo $02      'buffer(6)
'Byte Count          $04      'buffer(7)
'Data Hi             $00
'Data Lo             $0A
'Data Hi             $01
'Data Lo             $02
'Error Check         $__ (LRC or CRC) –– two bytes
'                    $__

    mbW0 = buffer(3)*255 + buffer(4) ' Calculate the starting address of registers (Holding registers are 16 bit)
    mbW0 = (mbW0 * 2) -1                   ' Claculate starting memory  byte to write to.... 2 bytes per holding register
    for mbB0 = 0 TO (buffer(7)-1)     ' buffer (7) contains the byte count
      mbB1 = buffer(mbB0 + 8)         ' Get byte of data
      'EPWrite mbW0,mbB1              ' Write data to EEPROM memory
      outbuffer(mbW0) = mbB1          ' write data to memory
      mbW0 = mbW0 +1                  ' increment memory pointer
      'wait 10 ms
    NEXT
'Response from slave
'Field Name (Hex)
'Slave Address        $0A     all ready in buffer(1)
'Function             $10     all ready in buffer(2)
'Starting Address Hi  $00    all ready in buffer(3)
'Starting Address Lo  $01     all ready in buffer(4)
'No. of Registers Hi  $00     all ready in buffer(5)
'No. of Registers Lo  $02     all ready in buffer(6)
'Error Check          $__(LRC or CRC) –– two bytes
'                     $__
Length = 6                    'Tell crc how many to calc
crc__16                       ' Calculate the CRC16 for response frame
'CRC field is appended to the message as the last field in the message.
'the low–order byte of the field is appended first, followed by the
'high–order byte.
buffer(length+1) = [byte]CRC    'crc16(1)
buffer(length+2) = CRC_H        'crc16(2)
Length = Length + 4
MaxDir = 1
For mbB0 = 1 To Length            ' Send the response to Master
  mbB1 = buffer(mbB0)
  Gosub charout
Next
MaxDir = 0
End Sub

Sub mbwriteBadRequest
'writeBadRequest:              ' Response for error in modbus poll
'the following message is sent as ascii and you can see what the crc of the master should be
' put the decimal value in the programmers calculator, switch to hex, and reverse the two bytes
' remember crc is low byte first, high byte second in the frame packet
MaxDir =1
hserprint "bad crc should be = "
hserprint crc
HSerPrintCRLF
MaxDir =0

if (MBFrame <> 0) then            ' If MBFrame = 0 then no response
  buffer(2)=buffer(1)+ 0x80        ' Set the error code in modbus frame
  buffer(3)=MBFrame - 0x80         ' Set the error nr
  Length = 3
  crc__16
  buffer(length+1) = [byte]CRC    'crc16(1)       ' Calculate the CRC16 for response frame
  buffer(length+2) = CRC_H        'crc16(2)
  Length = Length + 4
  MaxDir = 1
  For mbB0 = 1 To Length          ' Send the response to Master
    mbB1 = buffer(mbB0)
    Gosub charout
  Next mbB0
  MaxDir = 0
End if
End Sub

'readMB:
Sub SerialInterrupt

  If OERR   then                'OERR or  FERR   RC1STA.2 If USART error then clear the error flag
      CREN = 0                             'CREN
  end if
  If FERR   then                'OERR or  FERR   RC1STA.2 If USART error then clear the error flag
      CREN = 0                             'CREN
  end if

  CREN = 1

  if RCIF then                      ' RCIF  USART REC Interrupt (PIR1.5 = 1)
    TMR2Ticks = 0         ' reset time out which indicates end of MBFrame
    If (NewFrame = 1) OR (Length = 0) then      'New modbus frame start
      NewFrame = 0
      T2CON.2 = 1               ' Enable Timer2
      Length = 1
      End If

     do while RCIF               'Write modbus frame to buffer  (PIR1.5 = 1)
       buffer(Length) = RCREG
       Length = Length + 1
       if Length = 75 then
        Length = 0
       End If
     loop
  End If
End sub

Sub Timer2Interrupt
  if (TMR2IF = 1) then                        ' Timer2 interrupt flag
   TMR2IF = 0
   TMR2ON = 0                               ' Timer2 disable
   TMR2Ticks = TMR2Ticks + 1
     If TMR2Ticks > 120 then                     ' ~ 10 ms without new char
      NewFrame = 1                               'There was no new char on USART => end of modbus frame
     else
      TMR2ON = 1                                'Enable timer
     End If
  End If
  'Resume
End Sub

This is only RTU implementation not ascii. Only used HSer routines for developement and trouble shooting (some are left). It was easier to read and write to the USART. Modbus is a Master /Slave protocol. The Master asks for data or sends data and tells the slave where to put it. The commands sent to the slave and the data sent back from the slave are in packets starting with the slaves address and ending with a CRC16 check. I included some modbus documentation.

GL
Mike

[Anobium]

Very nice code. Excellent work.

Do have any photos of the opertional solution?

[mmotte]

I do have a few pics. Should I post them here or send them via other method? i will post one now

[Anobium]

Wonderful - can you send to Bed? And, I can we publish on the WebSite with some nice words?

[bed]

Took the challenge.
Thanks for sharing your work

[bed]

Article is online, now.
http://gcbasic.sourceforge.net/Typesetter/index.php/Modbus-Slave

[BASIL HATZILAIOS]

Mike,

about the code for modbus 3 and 16....I would like to use a PLC as master and a glcd as slave.....what modifications must do to above code modbus RTU slave, to work with PIC16F1939 ? the pic that work as slave is connected to a glcd, to diplay text that I send from PLC (modbus master)...so, what is the variable (Rx) that will checked for incoming data in above code ? the above code uses var outbuffer ....below is my first approach to slave code ....the code for writing to glcd is ok....just to setup pic uart for RS-485 and check for incoming ..
modbus slave ........initialize
glcd ......initialize
var( Rx)= modbus slave : check for incoming
locate glcd cursor ...... var ( Idx = total pixels of glcd ).....go to the begging of row
read holding register value.......var (pic_reg)=modbus slave: read holding reg (Idx)
print value to glcd......print (pic_reg)
modbus error loop .....if Rx=255 then output 1 to a pin .
an opinion for how to add the above code to glcd code...
thanks in advance,
Basil

[mmotte]

Basil,
First question is who is Master and who is slave. Who initiates the communication? Modbus Master sends the command and the slave sends the response. In my experience the slave was the PLC and my Distributed ControlSytem would send and receive from the Holding registers of the PLC thus making the DCS the master.

If you can make your PLC act as Master, then that is fine because everything you need is in the code for Modbus 3 and 16. Your PLC would send the command 16 (modbus 16 function (Preset Multiple Registers)) to the PIC with the data and you would simulate holding registers in the PIC . Remember the holing registers are 16bit words. Then you LCD part of the slave program would write it to the LCD.

     mbB1 = buffer(mbB0 + 8)  ' getting data from input buffer
  EPWrite mbW0,mbB1 ' Write data to EEPROM memory  'writing data to holding registers  or you LCD

Then the slave sends back the response confirming the transaction.. Header +the number of bytes and CRC16.

What brand and model PLC are you using?

I will help you through this.
Mike

[mmotte]

Basil,
I tried to comment and answer your questions in the above message.

"what modifications must do to above code modbus RTU slave, to work with PIC16F1939 ?"
Change the #chip 16F1939 ,8
define port for max485 direction
define usart port pins

"the pic that work as slave is connected to a glcd, to diplay text that I send from PLC (modbus master)..."
I am assuming you know how and where to make the PLC Master

"so, what is the variable (Rx) that will checked for incoming data in above code ?"
The master will send a command and it will be received in the " buffer()", It comes in as a data packet and when
the TMR2 times out it says the "Frame" Is received, Then the frame(all the bytes are in the buffer) is checked for address,
command, number of bytes, crc16 and then the command is executed. In your case ,Command 16, you would put the bytes
where you can use them for LCD display, Then a packet is sent back confirming reception.

"the above code uses var outbuffer"
outbuffer has nothing to do with the Modbus code, It is part of my DHT22 code only

"....below is my first approach to slave code ....the code for writing to glcd is ok...."
"just to setup pic uart for RS-485 and check for incoming .. modbus slave ........initialize"
usart baud blocking
set up pins tx, rx, dir
setup interrupts

"glcd ......initialize"
yours

"var( Rx)= modbus slave : check for incoming"
automatically comes in when frame is received complete

"locate glcd cursor ...... var ( Idx = total pixels of glcd ).....go to the begging of row"
what are doing with pixels?

"read holding register value.......var (pic_reg)=modbus slave: read holding reg (Idx)"
Your data is in the buffer and will be sent to your buffer with "Sub mbwriteRegResponse"
which processes the command 16

"print value to glcd......print (pic_reg)"
Your displaying the data

"modbus error loop .....if Rx=255 then output 1 to a pin ."
If errors occur then Modbus sends error message back to the master.

[BASIL HATZILAIOS]

Mike,
many thanks for your detailed answer...
The PLC is Schneider Modicon M221... PLC configured as master and the board with pic-glcd is the slave....from PLC we send a text that displayed to glcd...the communication starts from PLC that send commands and the slave responds.. .because my knowledge about GCB is limited , would you like to help me to merge the two codes?....Anobium has be done an excellent work to help me, and sends to me a code to write characters to a glcd with a pic(PIC16F1939)....I send you that demo code to add if it possible the part of modbus slave code....for now instead of master ( i'll get Modicon later ) I use ComTestPro as modbus master simulator to send commands to slave board.....is it possible to send larger characters to glcd, or ghraphics (bmp) ? for any other info please let me know...
thanks in advance.
Basil

[mmotte]

Basil,
Good information.

Are you making a message display or aiming for a HMI? Could you give a typical message?

I will look this over.

[BASIL HATZILAIOS]

Mike,
I made a modification to code , to display some text...just to test the code....I send you the modified code.... as glcd I use a 240x128 type AGM2412A ( DISPLAYTRONIC) with T6963C...for the hardware I use a PIC16F1939 , an RS-485 connector , an SN75176 as receiver/transmitter for modbus data, the glcd as above ....( If you need schematic please let me know), the connections pic-glcd are : port B to D0-D7 of glcd , RW to pin D.3 , RD to pin C.4, CE to pin C.5, CD to pin D.5, RESET to pin D.6 , FS to pin A.0........connections SN75176 to pic..: pin 1( R) to C.7 pin (RX)..pin 4(D) to pin C.6 (TX)...direction pin ( RE, DE) to pin A.1....

[BASIL HATZILAIOS]

Mike,
I send you a short video to see glcd with pcb that I was designed as modbus monitor....

[mmotte]

Basil,
This is what I had last night at 11pm.
It wouldn't compile for me because of LCD errors.... I am running 98.03GCB and don't have your GLCD in my library. There are more things I want to change in the interrupts but this is close to running.

I don't have your GLCD nor the PIC for a test bed

GL
Mike

[BASIL HATZILAIOS]

Mike,
very good work ...it compile for me, so can I send some characters with ComTestPro to test? is not critical for me the same type of glcd or pic...any type of glcd 240x128 even and 240x64 can be used ...Anobium make the code pic-glcd using a glcd 240x64....with a modification easy can work with 240x128....only to have controller T6963 or similar....I'll make some tests at next hours and inform you about....
best regards
Basil

[BASIL HATZILAIOS]

Mike,
I made some tests to send characters with ComTestPro...I had no response...I send 10 chars with mb command 16...as it seems at log there is no response with time out error...I was checked hardware for errors...ok...

[BASIL HATZILAIOS]

Mike,
the glcd screen after power on before send charcters..no change at tests...

[mmotte]

Basil,
I am working to put together a test board so I can get immediate feedback and trouble shoot.

What you sent looks correct. The time out could be the time out setting on comtestpro is 100 ms and had the scan really slow at 4sec

do Forever
        wait 4 s
      ' Modbus protocol function

Try increasing the comtestprotime out to 5000ms Or turn the wait down to something much lower. This would not be a solution but a test.

I probably need to take the "' Modbus protocol function" out and trigger it by itself. When a frame is complete.

I will work on this as I get time. I have to go to town today.

BR
Mike
I moved the processing of the Frame out of the main loop! See attached. This is a severely revised Version that I was working on last night. Worth a try.

[BASIL HATZILAIOS]

Mike,
I changed slave address to 07 to mb master according to code....the same ...no response...

[mmotte]

Basil,
The time out is beacuse of the setting on the comtestpro timeout in upper right corner 100ms and I had put the processing of the new fram in the display main loop which cycles at 4000ms.

I moved the processing of new frame to the interrupt of the mbtimer2match. this is not ideal but worth a try.

working at putting some hardware together so i can test here

BR
Mike

[BASIL HATZILAIOS]

Mike,
after change the mb slave address to 07 , I send 10 chars (ABCDEFGHIJ) , I had response error (time out) , but I had the chars on glcd as below ..

[BASIL HATZILAIOS]

Mike,
but in the next cycles chars changed as below.... I will try the updated code in a few minutes...

[mmotte]

That's exciting! We're close!

[BASIL HATZILAIOS]

Mike,
test for V1.55....the same as previous...responce error (time out) , 10 chars ok, but the first 4 chars changed in the next cycles....

[BASIL HATZILAIOS]

Mike,
hoping to help, I send you a code in C (for FC7), that works fine with a lcd 4x20 with modbus protocol...