Serial communication between 2 Microcontrollers

[basparky]

Hi All,

I have a dsPic (a) which communicaties with a Pic(b) over UART. The Dspic is the master and the Pic the slave. The slave(b) can be a unique device with his own data packet output.
In my current deisgn i have the slave sending his datapacket like following:

Code Select Expand

Proc SendMessage(Nr As Byte)
'Str = 255-3-200-0-100-100-233 wChecksum = 891 bCheckSUm = 123 
    StrToMain[0]    = 255           'Fixed ID
    StrToMain[1]    = Modus   
    StrToMain[2]    = Command     
    StrToMain[3]    = Throttle
    StrToMain[4]    = Dir
    StrToMain[5]    = SafetySwitch
    StrToMain[6]    = 233 'dummy           
    wCheckSum = StrToMain[0] + StrToMain[1] + StrToMain[2] + StrToMain[3] + StrToMain[4] + StrToMain[5]+ StrToMain[6]
    bCheckSum = wCheckSum.LowByte   
    StrToMain[7] = bCheckSum
   
    TMR0ON = 0
    TMR0IE = 0 
   
    For bIndex = 0 To 7
      HRSOut StrToMain [bIndex]
    Next
   
    Interval = 0             
    TMR0ON = 1
    TMR0IE = 1         
EndProc

The master is receiving like:

Code Select Expand

Isr U2RXInterrupt   
    ID = 255'121 'Id from joystick
       
    If U2STAbits_OERR = 1 Then
        Clear U2STAbits_OERR
        SOM = 0
        Index2 = 0
        GoTo ExitInterrupt2
    EndIf
       
    USART2bRx = U2RXREG   
   
    'catch start off message
    If USART2bRx = ID And SOM = 0 And Index2 = 0 Then
        SOM = 1
        Index2 = 0
    EndIf

    '   
    If SOM = 1 Then
        StrJoyStick[Index2] = USART2bRx
        Inc Index2
        If Index2 > 7 Then
            Index2 = 0
            ReceivedFromJoystick = 1
            SOM = 0
            Toggle LedRd
        EndIf
    EndIf
   
    ExitInterrupt2:
    Clear IFS1bits_U2RXIF
EndIsr


So the slave is sending his ID and a data packet in a fixed length. As shown the receiver waits for the ID 255 and then expects the payload before waiting for the next startbyte (ID).

I would like to make this communication more robuust and create somehow a ID based receive routine.
At this moment i have 3 types of slave. each with their own different datapacket and ID. Does anyone have some suggestions how to build this robuust?
I had issues with sending the SLaves ID because the value 255 van also be the value of one of the bytes in the payload. After knowing this i made a catch start off message as shown in the ISP but i think its too basic to have this working for 3 slave ID's.

I think i'm asking a direction and some help make this work in practise. I have no experience with dynamic data packages but believe this is what it should be on the receiver side.

Any hints or information how to do this would help me a lot. Thanks in advance!

[John Lawton]

You could use ninth bit addressing to indicate the packet start?

John

[trastikata]

Is it possible to include a MAC address to each packet?