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PIC24 RS232 Multiple byte read problem

 
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Loio



Joined: 22 Apr 2014
Posts: 3

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PIC24 RS232 Multiple byte read problem
PostPosted: Tue Apr 22, 2014 2:03 am     Reply with quote
Hi,

I am working with PIC24EP512GP806. I am trying to use UART of this PIC.

I have no problem with this code. I can read correct values from my computer.

Working correct code:
Code:

#include <24EP512GP806.h>

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES CKSFSM                   //Clock Switching is enabled, fail Safe clock monitor is enabled
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOJTAG                   //JTAG disabled


#device ICSP=3
#use delay(crystal=16000000)
#pin_select U1TX=PIN_G6
#pin_select U1RX=PIN_G8
#use rs232(UART1, baud=9600, stream=UART_PORT1)



void main()
{
   int8 serialData[15];
   int8 k=0;

   while(true)
   {
      if(kbhit() )
      {
         putc(getc());
      }
   }
}



However when I try to read multiple bytes (8 byte in code), It reads first byte always as 0xFF and shifts other bytes.

Here is the code,
Code:

#include <24EP512GP806.h>

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES CKSFSM                   //Clock Switching is enabled, fail Safe clock monitor is enabled
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOJTAG                   //JTAG disabled


#device ICSP=3
#use delay(crystal=16000000)
#pin_select U1TX=PIN_G6
#pin_select U1RX=PIN_G8
#use rs232(UART1, baud=9600, stream=UART_PORT1)




void main()
{
   int8 serialData[15];
   int8 k=0;

   while(true)
   
   {
   
      if(kbhit() )
      {
          for(k=0;k<8;k++)
         {
            serialData[k]=getc();
         }
         
         for(k=0;k<8;k++)
         {
            printf("%X",serialData[k]);
         }
      }
   }
}





And here is the sent and received values(hex).

1st Pack sent: 00 11 22 33 44 55 66 77
1st Pack Rec: FF 00 11 22 33 44 55 66

2nd pack sent: 00 11 22 33 44 55 66 77
2nd pack rec: 77 00 11 22 33 44 55 66

3rd pack sent: 00 11 22 33 44 55 66 77
2nd pack rec: 77 00 11 22 33 44 55 66

And I changed sent pack ;

4th pack sent: A0 A1 A2 A3 A4 A5 A6 A7
4th pack rec: 77 A0 A1 A2 A3 A4 A5 A6

5th pack sent: A0 A1 A2 A3 A4 A5 A6 A7
5th pack Rec: A7 A0 A1 A2 A3 A4 A5 A6

6th pack sent: A0 A1 A2 A3 A4 A5 A6 A7
6th pack Rec: A7 A0 A1 A2 A3 A4 A5 A6


I tought it maybe because of kbhit. I tried code below but result were same, always there is 0xFF as first byte and shifts others.



Code:

//if(kbhit() )
      {
          for(k=0;k<8;k++)
         {
            serialData[k]=getc();
         }
         
         for(k=0;k<8;k++)
         {
            printf("%X",serialData[k]);
         }



I think its a buffer problem. I tried to clear buffer before read data as in the code below. But no luck.

Code:

#include <24EP512GP806.h>

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES CKSFSM                   //Clock Switching is enabled, fail Safe clock monitor is enabled
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOJTAG                   //JTAG disabled


#device ICSP=3
#use delay(crystal=16000000)
#pin_select U1TX=PIN_G6
#pin_select U1RX=PIN_G8
#use rs232(UART1, baud=9600, stream=UART_PORT1)

#byte   U1STA=0x0222



void main()
{
   int8 serialData[15];
   int8 k=0;

   while(true)
   
   {
   
      bit_clear(U1STA,1);
      {
          for(k=0;k<8;k++)
         {
            serialData[k]=getc();
         }
         
         for(k=0;k<8;k++)
         {
            printf("%X",serialData[k]);
         }
      }
   }
}


Seems I am missing somethnig or I dont know thing
that causes this problem.

Can you help me to solve this problem? Have you faced such problem?

Thanks
Loio



Joined: 22 Apr 2014
Posts: 3

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PostPosted: Tue Apr 22, 2014 2:30 am     Reply with quote
I forget to add compiler version,


I use PCD v5.023
Ttelmah



Joined: 11 Mar 2010
Posts: 19480

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PostPosted: Tue Apr 22, 2014 2:55 am     Reply with quote
Let the RX line have time to go high _before_ you start trying to receive.
So:
Code:

#include <24EP512GP806.h>

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES CKSFSM                   //Clock Switching is enabled, fail Safe clock monitor is enabled
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOJTAG                   //JTAG disabled

#device ICSP=3
#use delay(crystal=16000000)
#pin_select U1TX=PIN_G6
#pin_select U1RX=PIN_G8
#use rs232(UART1, baud=9600, stream=UART_PORT1, NOINIT)

void main()
{
   int8 serialData[15];
   int8 k=0;
   delay_ms(20); //Allow time for the input to settle
   setup_uart(9600); //actually wake the UART

   while(true)
   {
      if(kbhit() ) //only actually means there is one character...
      {
          for(k=0;k<8;k++)
         {
            serialData[k]=getc();
         }
         
         for(k=0;k<8;k++)
         {
            printf("%X",serialData[k]);
         }
      }
   }
}

It looks like the classic problem where a MAX232, takes a little time to raise it's output line after starting. With your code as written (since there is nothing to mark the end of a packet etc..), it you start out of sync, you will stay out of sync forever. It sees the momentary 'low' as the start of a character, so receives a 0xff, from this.

As a comment, kbhit being 'true' implies one character is available. As written the code will then stall waiting for seven more characters to arrive...
Loio



Joined: 22 Apr 2014
Posts: 3

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PostPosted: Thu Apr 24, 2014 1:57 am     Reply with quote
Thanks Ttelmah, it solved my problem.

By the way, I dont use MAX232, I use FT232, also I tried Bluetooth-Rs232 Converter.

Thanks for your comment, Let me explain what I am plannig

I wanted to use kbhit instead of RS232 interrupt. PIC will have very short time loop in program and will check RS232 data always. When get 1sr char, will get other 7 ones too.

I will get rest of bytes with "timed getc()" function.

I will have Start and Stop bytes to check data pack.

Is it the Sync what you mentioned about, or is it somethnig other?

Thanks again Ttelmah








Thanks again
Ttelmah



Joined: 11 Mar 2010
Posts: 19480

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PostPosted: Thu Apr 24, 2014 2:23 am     Reply with quote
Seriously, 9600bps, implies characters arrive about 1/mSec. Your PIC can execute 8000 instructions between characters. For 8 characters, about 58000 instructions before they all arrive....
Not a 'very short time' at all....
jeremiah



Joined: 20 Jul 2010
Posts: 1342

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PostPosted: Thu Apr 24, 2014 6:23 am     Reply with quote
Just wanted to echo something Ttelmah mentioned. You use kbhit to see if a character is ready, but then read all 8 chars without re checking kbhit for each one. This is dangerous. In the event all 8 characters don't make it through, your code will hang until all 8 characters come, which might be the first byte(s) from your next block of 8. If it does that, you'll have accidentally split your block between 2 processing sessions, and that is probably the best case issue you'll run into. Depending on how the rest of your code works (I'm not sure how your processing loop works), you could hang forever.
bkamen



Joined: 07 Jan 2004
Posts: 1611
Location: Central Illinois, USA

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PostPosted: Thu Apr 24, 2014 9:41 am     Reply with quote
If you really want to do it right,

Write an ISR that handles incoming serial data into a FIFO.

Interrupts are your friend.

-Ben
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