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problem with RS232 in 12F675

 
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karthickiw



Joined: 09 Aug 2007
Posts: 82
Location: TN, India

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problem with RS232 in 12F675
PostPosted: Wed Mar 05, 2008 11:34 am     Reply with quote
hello..

i try to write the program to send the Hex command through PIC12F675, but i dont receive the any command from PIC...


my complier version is IDE - 3.41
PCB - 3.185
PCM -3.185
PCH - 3.185


Code:
#include <12F675.h>
#device adc=8
#use delay(clock=4000000)
#fuses NOWDT,INTRC_IO, CPD, PROTECT, NOMCLR, PUT, BROWNOUT
#byte OSCCAL=0x90
#define GP0 PIN_A0
#define GP1 PIN_A1
#define GP2 PIN_A2
#define GP3 PIN_A3
#define GP4 PIN_A4
#define GP5 PIN_A5
//========================
#use rs232(baud=9600,parity=N,xmit=PIN_A4,rcv=PIN_A5,bits=9)


#byte ADCON0 = 0x1F
#byte ANSEL = 0x9F
#byte CMCON = 0x19

#rom 0x3ff = {0x3470} // input the calibration code
void main()
{

ADCON0 = 0; // ADC off
ANSEL = 0; // GPIO pins 0,1,2 and 4 set to all digital
CMCON = 7; // Comparators off
set_tris_a(0b100000);
delay_ms(1000);
putc(0X7E);
putc(0X07);
putc(0XA0);
putc(0X30);
putc(0X30);
putc(0X30);
putc(0X30);
putc(0X30);
putc(0X7E);

while(1) {



    }

}



please check the code and give solution...
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Mar 05, 2008 12:21 pm     Reply with quote
Why are you using 9 bits ? Standard RS-232 is 8 bits. You don't need
to specify 8 bits in the #use rs232() statement. It's the default value.

Are you using a MAX232 chip ?

See these two threads for more help.
http://www.ccsinfo.com/forum/viewtopic.php?t=32751
http://www.ccsinfo.com/forum/viewtopic.php?t=28067
Guest
PostPosted: Wed Mar 05, 2008 3:52 pm     Reply with quote
no, I am using 8 bit, it goes through MAX485,
but the problem arises only with a 20MHz crystal,
it works perfectly with a 10MHz crystal.

So the only logical conclusion is the baud rate generator.

The core is: how to set the baud rate generator manually?
Why it doesn't work, and why the IDE shows 0 for the register
involved and manually set?
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Mar 05, 2008 4:04 pm     Reply with quote
There is no baud rate generator in a 12F675. It doesn't have a UART.
It's all done with software polling loops and delays, in the CCS library code.
Ttelmah
Guest
PostPosted: Wed Mar 05, 2008 4:57 pm     Reply with quote
And (of course), _requires_ that you set the #use delay, to match the frequency the chip is actually running. You talk about using 10MHz, and 20MHz, but the code shown, is for 4Mhz. Remember also the HS fuse. I have seen chips run at 10MHz, with XT selected, but then fail when trying to go faster. What voltage is the power supply?. 20Mhz, requires at least 4.5v.

Best Wishes
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