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rs-232 out not good

 
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ferrarilib



Joined: 11 Jun 2005
Posts: 38

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rs-232 out not good
PostPosted: Sat Jun 11, 2005 4:32 am     Reply with quote
Hallo I am Mauro.
I am trying CCS c compiler and I don't know how work fine.

my code is simply this:
Code:

#include <16F877a.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=40000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
void main() {

while(1)
{

putc('U');
}

}

I have Max232 and C7->Rx e C6->Tx
The output isn't UUUU.
but
0x1F 0x1F 0x1F 0x1F 0x1F 0x1F 0x1F 0x1F
continuous...

I have tried with another Hex with another compiler and all is fine.

What can be my problem ?

Thanks
Ttelmah
Guest
PostPosted: Sat Jun 11, 2005 5:07 am     Reply with quote
The problem is your clock rate.
The 16F877a, has a maximum clock rate of 20MHz. Your '#use delay' line, is saying that the clock is running at 40MHz. This line is used for delays, but also to calculate the timings for the serial port. As such, the division is being set up based on an incorrect clock rate, and the data is coming out far slower than it should do. Looking at the values seen, I'd 'guess' that a single bit of the outgoing stream is being seen as five bits by the receiver, suggesting that your actual clock rate is perhaps about 8MHz.
Check your crystal frequency, correct the line, and it should work.

Best Wishes
ferrarilib



Joined: 11 Jun 2005
Posts: 38

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PostPosted: Sat Jun 11, 2005 7:14 am     Reply with quote
Ttelmah wrote:
The problem is your clock rate.
The 16F877a, has a maximum clock rate of 20MHz. Your '#use delay' line, is saying that the clock is running at 40MHz. This line is used for delays, but also to calculate the timings for the serial port. As such, the division is being set up based on an incorrect clock rate, and the data is coming out far slower than it should do. Looking at the values seen, I'd 'guess' that a single bit of the outgoing stream is being seen as five bits by the receiver, suggesting that your actual clock rate is perhaps about 8MHz.
Check your crystal frequency, correct the line, and it should work.

Best Wishes



Thanks !! Very Happy Very Happy
now is all good !
was 8MHz clock
thanks
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