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che_chia
Joined: 09 May 2011
Posts: 6
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| Can't tx correct data in the 1st time tx of RS-485 |
 Posted: Thu May 19, 2011 2:55 am |
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I can not transmit the correct data in the 1st transmission. It means if I transmit the same data 2 times, I can see the correct data was sent in the 2nd transmission.
Why is the reason that I can transmit the correct data in the 1st transmission?
| Code: |
#include <16F1947.H>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT
#Fuses INTRC_IO
#use delay(clock=32000000)
#use rs232(baud=115200, xmit=PIN_C6, rcv=PIN_C7, bits=8)
unsigned int uchCRCHi, uchCRCLo;
unsigned int8 TXDBuffer[8];
unsigned int8 TXCnt=0;
void main (void)
{
while(1)
{
if (TXCnt<=1)
{
TXCnt++; // if (TXCnt<=2). I can see the correct data in TXCnt=2
TXDBuffer[0]=0xB5;
TXDBuffer[1]=0x00;
TXDBuffer[2]=0x74;
TXDBuffer[3]=0x65;
TXDBuffer[4]=0x73;
TXDBuffer[5]=0x74;
TXDBuffer[6]=0x00;
TXDBuffer[7]=0x00;
output_bit(PIN_G0,1);
putc( TXDBuffer[0] );
putc( TXDBuffer[1] );
putc( TXDBuffer[2] );
putc( TXDBuffer[3] );
putc( TXDBuffer[4] );
putc( TXDBuffer[5] );
putc( TXDBuffer[6] );
putc( TXDBuffer[7] );
delay_us(2000);
output_bit(PIN_G0,0);
}
}
} |
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temtronic
Joined: 01 Jul 2010
Posts: 9221
Location: Greensville,Ontario
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| Posted: Thu May 19, 2011 5:12 am |
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Are you using RS-485 as in the subject line , or RS-232 as your program indicates ?
If really using RS-485, you must specify the 'control pin' in the USE RS232(options...) statement.
Also you should add the 'errors' option to the USE RS232(...) in all cases of using the internal hardware UART.
Also, confirm that the device that you're transmitting the data to is setup correctly as the PIC is only 1/2 of the 'system'. |
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che_chia
Joined: 09 May 2011
Posts: 6
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| Posted: Thu May 19, 2011 5:32 am |
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Dear all,
how can I clear the buffer of RX and TX? |
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temtronic
Joined: 01 Jul 2010
Posts: 9221
Location: Greensville,Ontario
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| Posted: Thu May 19, 2011 7:01 am |
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If using the internal hardware UART..
You have to read the RX buffer, twice to 'clear' it...
You have to send the TX buffer, once to clear it...
as there is no command to 'clear' the internal shift registers used for serial I/O, not that I'm aware of.
Maybe newer PICs, but unlikely. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19499
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| Posted: Thu May 19, 2011 10:22 am |
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Forget about 'clearing buffers'.
The RX buffer you can clear by reading characters, and the TX buffer will clear with time, or you can just poll the INT_TBE line, if you want to know when it is empty. You don't have to 'send the TX buffer once', it clears itself. Once loaded, it _automatically sends_.
However these should not be a problem.
Key thing is to describe the RS485 hardware. How are you handling the enable pin?. Is the bus 'biased' when not in use?. Is it going through other transceiver devices?.
I'd suspect that the bus is floating when not driven, so an infinite stream of garbage is being seen by the receiving device, which takes time to recover from this.
Describe the hardware.
Best Wishes |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Thu May 19, 2011 4:52 pm |
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Make sure the 485 bus is in a valid stop bit state when no one is driving it. If it is already in a start bit state when someone tries to put a start bit on it, the receiver will never see the beginning of the start bit.
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