Can anybody help me?
When I am receiving a char from Pc to 8051 via Serial port, I am using a circular buffer. But it does not work as it should. When an interupt is triged an interupt rutine com_isr is called. With function com_getchar I read a char from a circular buffer. Everything worked ok, before i implemented a circular buffer. Buffer size is 64.

void com_isr () /*interrupt 4 using 2*/
{
/*------------------------------------------------
Received data interrupt.
------------------------------------------------*/

if (RI != 0)
{
RI = 0;

if (r_in!=63) {
if ((r_in + 1) != r_out) {rbuf[r_in++]=SBUF;}}

else {
r_in=0;
if ((r_in + 1) != r_out) {rbuf[r_in++]=SBUF;}
}
}

/*------------------------------------------------
Transmitted data interrupt.
------------------------------------------------*/
if (TI != 0)
{
TI = 0;

if (t_out!=63){
if (t_in != t_out)
{SBUF = tbuf[t_out++];}
else
t_disabled = 1;
}
else {
t_out=0;
if (t_in != t_out)
{SBUF = tbuf[t_out++];}
else
t_disabled = 1;
}
}
}


char com_getchar()
{
char c;

if (com_rbuflen () == 0)
return (-1);

EA = 0; /* Disable Interrupts */

if (r_out!=63) {c=rbuf[r_out++];}
else {r_out=0;
c=rbuf[r_out++];}
EA = 1; /* Enable Interrupts */

return (c);
}


Thanks in advance!