PIC18F452 with 40.685 Mhz OSC

[mesuty]

Dear Friends;

In my project , I have a PC communicating 30 PIC 18F452 over a four wire RS 422 circuit. Level converter is 2x Max 485 one for TX and other is RX. Enable PIN of RX circuit is directly connected to logic 0 to keep all devices in listen mode. TX of PICS are controlled with PIN_C1. I am using hardware UASRT with 9600 Baud and OSC frequency of PIC is 40.685 MHZ.

For the trial purposes , just a PC and one PIC are connected to comms. line. The RX and TX lines are terminated with 120 ohms at PIC side.

When I start the circuit , I am receiving many garbage charecters. After a few charecters sent , transmision pausing as stated in delay_ms(400); . So the routine is working.

My Compiler version is 3.221.

Could someone help me ?

My test routine is as follows.

#include <18F452.h>
#device adc=8
#use delay(clock=40685000)
#fuses NOWDT,WDT128,HS, NOPROTECT, NOOSCSEN, BROWNOUT, BORV20, NOPUT, STVREN, NODEBUG, NOLVP, NOWRT, NOWRTD, NOWRTB, NOWRTC, NOCPD, NOCPB, NOEBTR, NOEBTRB
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=9,stream=MAINCOMM)


void main()
{

set_tris_D(0x00);
set_tris_E(0x00);
set_tris_C(0b10110000);
output_high(PIN_C1); // TX control pin

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_8_bit);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_2);
setup_timer_2(T2_DIV_BY_1,255,16);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
enable_interrupts(INT_TIMER0);
enable_interrupts(INT_TIMER1);
enable_interrupts(INT_TIMER2);
enable_interrupts(INT_TIMER3);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
output_high(PIN_C1);
while(1)
{
putC('a');
delay_ms(400);
}
}

[ckielstra]

Your #fuses statement is wrong and possibly your clock source too.

Running at 40MHz is only possible with:
1) A 10MHz crystal and enabling the 4xPLL clock multiplier (replace HS by H4 in the #fuses statement).

or

2) An external clock generator and setting the #fuses statement to EC i.s.o. HS.

Check table 22-4 (page 271) of the PIC18Fxx2 manual.


Another problem in your program is that you are activating a lot of interrupts, but you have no interrupt handlers. So once an interrupt becomes activated it's never cleared and effectively stalls your program.

[mesuty]

My CPU is working without any problem with HS mode and 40.685 Mhz OSC. Do you think is there a method to communicate at any baud rate, just for trial purposes.

BR.

[Ttlemah]

From what you describe, your problem could be line bias. An undriven differential pair like this, is _not_ warranted to float to a '0' ('1' at the PIC) state. You can get differential driver/receivers, that are warranted to do this, or differential terminators that do this. Alternatively, just use a resistive divider terminator. So (for 100ohm termination, rather than 120ohm), use:

[Mesuty]

Thank to everbody replied;

Everythink seems OK now.

B.R.