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RS232 problem with PIC18f452

 
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Guest
RS232 problem with PIC18f452
PostPosted: Wed Dec 22, 2004 9:57 pm     Reply with quote
I am using a serial LCD to debug my PIC programs.
I have been using it fine with the PIC16f84a which has no hardware USART. Since the PIC and the serial LCD were directly wired, I used the INVERT option.

Now, I am trying to use a PIC18f452, which has a hardware USART. I don't want to use the software USART (by changing the xmit pin or using the option FORCE_SW).

The problem is that the LCD is getting garbage characters. How can I fix this problem???.

Here is some code snipet:

Code:
#include <18F452.h>
#device adc=8
#use delay(clock=4000000)
#fuses NOWDT,WDT128,XT, NOPROTECT, NOOSCSEN, BROWNOUT, BORV20, NOPUT, STVREN, NODEBUG, NOLVP, NOWRT, NOWRTD, NOWRTB, NOWRTC, NOCPD, NOCPB, NOEBTR, NOEBTRB
#use rs232(baud=2400,parity=N,invert,xmit=PIN_C6,rcv=PIN_C7,bits=8)



Code:
#define COUNT_TO 31
byte count;
unsigned int num;
int printmsg;

void clearScreen(void);

#INT_RTCC
clock_isr() {
   if(--count==0) {
      num++;
      count = COUNT_TO;
      printmsg = 1;
   }
}

void main()
{

   setup_adc_ports(NO_ANALOGS);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(FALSE);
   setup_wdt(WDT_OFF);
   setup_timer_0(RTCC_INTERNAL);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
   setup_timer_3(T3_DISABLED|T3_DIV_BY_1);

      count = COUNT_TO;
   num = 0;
   printmsg = 1;
   
   /* give plenty of time to the LCD to initialize */
   delay_ms(1000);

   set_rtcc(0);
   setup_counters(RTCC_INTERNAL, RTCC_DIV_128);
   enable_interrupts(INT_RTCC);
   enable_interrupts(GLOBAL);

   while(1) {
      if (printmsg) {
         clearScreen();
         printf("Count: %u", num);
         printmsg = 0;
      }   
   }
}

void clearScreen(void)
{
   putc(254);
   putc(1);
return;
}
Guest
PostPosted: Wed Dec 22, 2004 9:59 pm     Reply with quote
I forgot... This program is supposed to count seconds.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Dec 22, 2004 10:55 pm     Reply with quote
Have you really compiled this code ? If I try to compile your program,
the line below causes this error message:
"USE parameter value is out of range H/W USART can not invert"
Code:
#use rs232(baud=2400,parity=N,invert,xmit=PIN_C6,rcv=PIN_C7,bits=8)
Guest
PostPosted: Thu Dec 23, 2004 8:43 am     Reply with quote
You get this error message because of the invert in the fuse statement. If you remove that invert option, the code compiles fine.

Anyway, I did get it to count seconds and display the result correctly on the LCD by forcing the compiler to use the Software USART on C6 and C7 pins.

But I was hoping there was another way to do this (using just hardware USART).

here is the most updated version of the code (working)

Code:
#include <18F452.h>
#device adc=8
#use delay(clock=4000000)
#fuses NOWDT,WDT128,XT, NOPROTECT, NOOSCSEN, BROWNOUT, BORV20, NOPUT, STVREN, NODEBUG, NOLVP, NOWRT, NOWRTD, NOWRTB, NOWRTC, NOCPD, NOCPB, NOEBTR, NOEBTRB
#use rs232(baud=2400,parity=N,xmit=PIN_C6,rcv=PIN_C7,FORCE_SW,invert,bits=8)



Code:
#define COUNT_TO 31
byte count;
unsigned int num;
int printmsg;

void clearScreen(void);

#INT_TIMER0
clock_isr() {
   if(--count==0) {
      num++;
      count = COUNT_TO;
      printmsg = 1;
   }
}

void main()
{

   setup_adc_ports(NO_ANALOGS);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(FALSE);
   setup_wdt(WDT_OFF);
   setup_timer_0(RTCC_INTERNAL | RTCC_DIV_128 | RTCC_8_BIT);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DISABLED,0,1);
   setup_timer_3(T3_DISABLED|T3_DIV_BY_1);

      count = COUNT_TO;
   num = 0;
   printmsg = 1;
   
   /* give plenty of time to the LCD to initialize */
   delay_ms(1000);

   set_timer0(0);
   enable_interrupts(INT_TIMER0);
   enable_interrupts(GLOBAL);

   while(1) {
      if (printmsg) {
         clearScreen();
         printf("Count: %u", num);
         printmsg = 0;
      }   
   }
}

void clearScreen(void)
{
   putc(254);
   putc(1);
return;
}
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Thu Dec 23, 2004 11:25 am     Reply with quote
The hardware UART doesn't support the invert option. Sending non-inverted data to the LCD will result in garbage.
Inverting the data yourself before sending it to the hardware UART won't work because the start- and stopbits will still be non-inverted. Your only option for using the hardware UART is to add an hardware inverter (cheap).
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