Serial Communication Problem

[mister_e]

Here's something to play with.

    '   Program to echo incoming serial data 
    '   Baudrate : 2400 Bauds
    '   Method :   Polling USART interrupts flags

    '   Pic Definition
    '   ==============
        ' Using PIC 18F2320 @ 4MHZ and bootloader
        '
        DEFINE LOADER_USED 1
        DEFINE OSC 4
        
    '   Hardware configuration
    '   ======================
        '
        '
        TRISC  = %10000000    ' PORTC.7 is the RX input
                              ' PORTC.6 is the TX output
    
    '   Serial communication definition
    '   ===============================
        ' Using internal USART and MAX232 to interface to PC
        '
        RCSTA = $90 ' enable serial port, 
                    ' enable continuous receive
                    '
        TXSTA = $24 ' enable transmit, 
                    ' BRGH=1
                    '
        SPBRG = 103 ' set baudrate to 2400                   
        
    '   Alias definition
    '   ================
        '
        '
        RCIF VAR PIR1.5     ' Receive  interrupt flag (1=full , 0=empty)
        TXIF VAR PIR1.4     ' Transmit interrupt flag (1=empty, 0=full)
        OERR var RCSTA.1    ' Overrun error
        CREN var RCSTA.4    ' Continuous receive
                
    '   Hardware initialisation
    '   =======================
        '
        '
        pause 10 ' safe start-up delay
    
Main:
    if oerr then  ' Overrun error?
       cren=0     ' clear it
       cren=1
       endif

    if RCIF then    ' incomming data?
       TXREG=RCREG  ' take it, send it
       while TXIF=0 ' wait untill transmit buffer is empty
       wend
       endif
    goto main

the following use HSERIN/HSEROUT statement. Since your PIC have internal USART... why not using it

    '   Program to echo incoming serial data 
    '   Baudrate : 2400 Bauds
    '   Method :   Polling USART interrupts flags

    '   Pic Definition
    '   ==============
        ' Using PIC 18F2320 @ 4MHZ and bootloader
        '
        DEFINE LOADER_USED 1
        DEFINE OSC 4
        
    '   Hardware configuration
    '   ======================
        '
        '
        TRISC  = %10000000    ' PORTC.7 is the RX input
                              ' PORTC.6 is the TX output
    
    '   Serial communication definition
    '   ===============================
        ' Using internal USART and MAX232 to interface to PC
        '
        DEFINE HSER_RCSTA 90h ' enable serial port, 
                              ' enable continuous receive
                              '
        define HSER_TXSTA 24h ' enable transmit, 
                              ' BRGH=1
                              '
        define HSER_SPBRG 103 ' set baudrate to 2400                   
        DEFINE HSER_CLOERR  1 ' automatic clear overrun error  
        
    '   Alias definition
    '   ================
        '
        '
        RCIF VAR PIR1.5     ' Receive  interrupt flag (1=full , 0=empty)
        TXIF VAR PIR1.4     ' Transmit interrupt flag (1=empty, 0=full)
        
    '   Variable definition
    '   ===================
        '
        '
        SerialData var byte
        
    '   Hardware initialisation
    '   =======================
        '
        '
        pause 10 ' safe start-up delay
    
Main:
    if RCIF then            ' incomming data?
       hserin  [Serialdata] ' take it
       hserout [serialdata] ' send it
       endif
    goto main

hope this help

[elec_mech]

Mister_E,

Thank you for the lovely code! It works nicely and I've been examining it while referencing the datasheet and I have learned a good deal. I then tried to manipulate it to work with my application and I've hit a wall. Initially I'm trying to look at a string of characters sent via the hyperterminal, particularly the first and last bit.

Now, perhaps I'm going into overkill with caution, but I only want to store the string into a variable array if the string starts with a ASCII "!". I then want to continue taking the rest of the string until an ASCII "L" is seen.

The idea being if for some reason or another, I receive a string of data and I start storing the data string at the middle instead of the beginning and miss some data. Here's what I have:

' Program to echo incoming serial data
' Baudrate : 2400 Bauds
' Method : Polling USART interrupts flags

' Pic Definition
' ==============
' Using PIC 18F2320 @ 4MHZ and bootloader
'
DEFINE LOADER_USED 1
DEFINE OSC 4

' Hardware configuration
' ======================
'
'
TRISC = %10000000 ' PORTC.7 is the RX input
' PORTC.6 is the TX output

' Serial communication definition
' ===============================
' Using internal USART and MAX232 to interface to PC
'
DEFINE HSER_RCSTA 90h ' enable serial port,
' enable continuous receive
'
define HSER_TXSTA 24h ' enable transmit,
' BRGH=1
'
define HSER_SPBRG 103 ' set baudrate to 2400
DEFINE HSER_CLOERR 1 ' automatic clear overrun error

' Alias definition
' ================
'
'
RCIF VAR PIR1.5 ' Receive interrupt flag (1=full , 0=empty)
TXIF VAR PIR1.4 ' Transmit interrupt flag (1=empty, 0=full)
a var byte
i var byte
' Variable definition
' ===================
'
'
SerialData var byte[40]

' Hardware initialisation
' =======================
'
'
pause 10 ' safe start-up delay

Main:
' Clear - tried using this to clear, but then I get nothing back

if RCIF then ' incomming data?
hserin [SerialData[0]] 'Store the first character received in SerialData,
'at byte 0
endif

if SerialData[0] = "!" then RCV 'if the first byte is an ASCII ! then
'go on to receive rest of data string


goto Main


RCV:

for i = 1 to 40

hserin [SerialData[i]] ' take it
if SerialData[i] = "L" then TRS 'if an ASCII L is
'present stop
'and output
'string
next

goto Main 'If ASCII L is not detected return to main loop


TRS:
for a = 1 to i 'Okay, if I set a = 0 to i, I get a ! in
'front of everything when it outputs
'i.e. if I send !#00CL I get !!#00CL
'back. Why, I don't know.
hserout [SerialData[a]] ' send it
next 'endif
hserout [10,13] 'line feed and carriage return
goto Main





Alright, if I send !#X00CL I get back !#X00CL, which is great! However, and here's the where the confusion starts, if I send 123456ABCDEF#, I get nothing back, again, good news right? But, if I follow that string with !#X00CL, I get back 123456ABCDEF#!#X00CL. I am hitting a wall here.

It seems as though the program stores up to 41 (0 to 40) bytes from a serial string (this because in my code I set SerialData to store up to 41 bytes, from 0 to 40). Once it sees 41 bytes, it resets itself and starts anew until it sees an ASCII L. For example, if I send 123456ABCDEF# three times then follow with !#X00CL I get back #1X00CL.

Is there a way to tell the program to write and erase to only SerialData[0] until a specific character is seen? ASCII ! in this case. Or am I missing something else altogether? Thanks!

[mister_e]

this should give you a hand!

    '   Program to echo incoming serial data 
    '   Baudrate : 2400 Bauds
    '   Method :   Polling USART interrupts flags

    '   Pic Definition
    '   ==============
        ' Using PIC 18F2320 @ 4MHZ and bootloader
        '
        DEFINE LOADER_USED 1
        DEFINE OSC 4
        
    '   Hardware configuration
    '   ======================
        '
        '
        TRISC  = %10000000    ' PORTC.7 is the RX input
                              ' PORTC.6 is the TX output
    
    '   Serial communication definition
    '   ===============================
        ' Using internal USART and MAX232 to interface to PC
        '
        RCSTA=$90 ' enable serial port, 
                  ' enable continuous receive
                  '
        TXSTA=$24 ' enable transmit, 
                  ' BRGH=1
                  '
        SPBRG=103 ' set baudrate to 2400                   
        DEFINE HSER_CLOERR   1 
        
    '   Alias definition
    '   ================
        '
        '
        RCIF VAR PIR1.5     ' Receive  interrupt flag (1=full , 0=empty)
        TXIF VAR PIR1.4     ' Transmit interrupt flag (1=empty, 0=full)
        CREN var RCSTA.4    ' Receiver enable bit
        
    '   Variable definition
    '   ===================
        '
        '
        SerialString var byte[40]
        Counter      var byte
        Success      var bit
        i            var byte
        
    '   Hardware initialisation
    '   =======================
        '
        '
        pause 100 ' safe start-up delay

Main:
   clear
   if RCIF then               ' incomming data?
      I=RCREG                 ' take it
      if i !="!" then discard ' is it the header character?
      Redo:
          hserin 500,discard,[i]  ' get next character, if it's too long
                                  ' get out of here and wait the next header
                                  ' character
                                  '
          if i ="L" then discard  ' is it the end?
          serialstring[counter]=i ' Store into the array
          counter=counter+1       '
          goto Redo      
      Discard:
              if i="L" then success=1 ' Yeah i got a valid string
      endif
  
   if success then
      cren=0  ' Disable Receiver
      hserout ["String received : ",str serialstring\counter,13,10,_
               "Character count : ", dec counter,13,10]
      cren=1  ' Enable receiver
      endif
   goto main

[elec_mech]

Steve,

Thank you for the code, it worked beautifully. I did notice that moving the clear command down to the very bottom right before the 'goto main' worked better. I think the data came in so fast that if the timing were off I missed some data streams.

I have a question regarding the clear command. I understand it completely clears the ram which prevents a constant repeating loop of a single data input stream. Is there another way to specifically clear or erase whatever register or ram location the USART uses? I ask because I am running several if then statements that require checking the status of certain variables and if I use the clear command, I lose the original status/data in those variables.

I've tried using RCIF = 0 and RCREG = 0 to no avail. I've also tried the ERASECODE $FAEh to clear the RCREG register, but this command doesn't work in PicBasic Pro with the 18F2525 chip I'm using. Any suggestions?

Again, thanks again for the code, I've been playing with it all day, making mistakes, gaining victories and generally learning a lot in the process.

[mister_e]

You're welcome.

You'll clear then RCREG by reading it 2 times

TempVar=RCREG
TempVar=RCREG

[elec_mech]

Upon having another set of eyes look at my code and using the debugger I'm learning to use slowly with more interest, I forgot to clear the counter and i variables. Effectively it was continuing to loop because those variables still had values assigned. Thank you for your time and help Steve, I do appreciate it.

To anyone else who may be interested in receiving a serial string, reading it and then doing something based upon a character(s) received, let me know and I'll post some really nice code to play with.

Thanks again to Joe, Luciano, and Steve. I learned a great deal by all the info and code posted.

[Dalomir]

I put the schematic in the attachement of this post.

Its an usart with 2 PIC18F452 linked together by PIN 25 and PIN 26

One receive a paralelle 4 bits number from a numerical keyboard, light LED at PIN 2, 3, 4, 5, 6, 8, 9 and 10 to show that number and send that number directly to the other PIC RX PIN.

Thats other PIC then receive that serial number and lights LED in the same way as the other PIC, showing that the number was successfully sent.

If anyone has a code that would make it work, I would really appreciate.

[leemin]

To anyone else who may be interested in receiving a serial string, reading it and then doing something based upon a character(s) received, let me know and I'll post some really nice code to play with.

yupe. i need a program to receive a serial string, reading it and then doing something. my string is something like this X-Addr-Mode-Data(30bytes)-Y
where X stand for SOT and Y stand for EOT. Addr is use to indicate the dedicated address value i want to send data.

my code is something like below:
include "modedefs.bas"
DEFINE SHIFT_PAUSEUS 20
define OSC 20
DEFINE HSER_CLOERR 1 ' automatic clear overrun error

TRISA=%11110000
TRISB= %11111011
TRISC.6 = 1
TRISC.7 = 0

symbol Addr_Data_In=porta.4
symbol en=porta.3
symbol stb=porta.2
symbol clk=porta.1
symbol data_out=porta.0

SPBRG = 32 ' Set baud rate to 9600
RCSTA = $90 ' Enable serial port and continuous receive
TXSTA = $24 ' Enable transmit and asynchronous mode
RCIF VAR PIR1.5 ' Receive interrupt flag (1=full , 0=empty)
TXIF VAR PIR1.4 ' Transmit interrupt flag (1=empty, 0=full)
OERR var RCSTA.1 ' Overrun error
CREN var RCSTA.4 ' Continuous receive
ADCON1=6

display: if RCIF then
i=RCREG
if i != "X" then discard

redo: hserin 500,discard,[i]
if i="Y" then discard
serialstring[counter]=i
counter=counter+1
goto redo

discard: if i="Y" then success=1
endif
if success then
cren = 0
if (serialstring[0] <> address_Value) then reset
if serialstring[1] = $30 then turn_off_led
serialstring[2]=a29
serialstring[3]=a28
serialstring[4]=a27
serialstring[5]=a26
serialstring[6]=a25
serialstring[7]=a24
serialstring[8]=a23
serialstring[9]=a22
serialstring[10]=a21
serialstring[11]=a20
serialstring[12]=a19
serialstring[13]=a18
serialstring[14]=a17
serialstring[15]=a16
serialstring[16]=a15
serialstring[17]=a14
serialstring[18]=a13
serialstring[19]=a12
serialstring[20]=a11
serialstring[21]=a10
serialstring[22]=a9
serialstring[23]=a8
serialstring[24]=a7
serialstring[25]=a6
serialstring[26]=a5
serialstring[27]=a4
serialstring[28]=a3
serialstring[29]=a2
serialstring[30]=a1
serialstring[31]=a0
endif
reset: cren=1 ' Enable receiver
goto display