#use RS232 BAD TIMMING ??

[Horizonlight]

Hi !

I use this code to send data at 250KBaud, when a check with a scope i got
4US bit time for 1 and 2.8us for 0 ???

I have make many test with Usart ans software usart , i got 2.8us on 0 ?
i have try many Pic !!!

Thanks for your help !!!

#include <16f876>

#USE Delay(Clock=20000000)
#use rs232(baud=250000, xmit=PIN_c6, bits=9,errors)
#bit ninth_bit = RS232_ERRORS.7
#DEFINE H_START 10
#BYTE Port_B = 0x06
#BYTE Port_A = 0x05
#BYTE Port_C = 0x07
#byte port_d = 0x08
#byte port_e = 0x09
#define ints_per_second 2
#use fast_io(c)
#use fast_io(a)

byte secounds;
byte int_count;

byte Receive, i;
long address;
long aa;
byte b;
byte h_count;

#int_rtcc
clock_isr(){
byte a;
long b;
if(--int_count==0) {
//output_low(pin_a0);
//delay_us(88);
//output_high(pin_a0);
//delay_us(8);

putc(170);
putc(0);
int_count=ints_per_second;

}
}



main(){
byte a;
ninth_bit =1;
set_tris_a(00000);

//set_tris_c(00000000);

port_b_pullups(true);

int_count=ints_per_second;
set_rtcc(0);

setup_counters(rtcc_internal, rtcc_div_256);
enable_interrupts(int_rtcc);
enable_interrupts(global);

output_high(pin_c7);
start:

delay_ms(5);
goto start;



}

[Ttelmah]

Ignoring everything else, how are you getting the figure '2', for 'INTS_PER_SECOND'?. If you chip is running at 20MHz, as set in your delay statement, then the RTCC, should interrupt 76 times per second (20000000/(4*256*256)). If it is interrupting 2 times per second, then your system clock, is only 500KHz....
With only one pin given in the RS232 setup line, the soft UART will allways be selected. However the timings of both, are completely dependant, on your actual clock frequency matching the delay setting.
As seperate comments, use the 'code' button to post code. Also consider 'tidying' your programming style. Goto jumps are 99%unneccessary, and can encourage program layouts that are likely to fail. They should only be used when they bring a real advantage. When posting 'problem' code, remove the 'dross', but leave the working core. You have loads of variable declarations, and defines that are not used, but have left out the fuses, so the code as posted cannot run.

Best Wishes

[PCM programmer]

I stripped your program down to essentials, compiled it with PCM 3.249,
and programmed it into a PicDem2-Plus board. I measured 4.18 us for
a "high" bit and 3.36 us for a "low" bit. That's with the software UART.
Here's the program I tested it with: