Try this circular buffer,

#define SLEN 64
unsigned char xdata serin_buff[SLEN];
unsigned char data sihead,sitail;

initialize:
sihead = sitail = 0;

to store data:
serin_buff[sihead++ & (SLEN-1)] = SBUF;

to get data:
tmp = serin_buff[sitail++ & (SLEN-1)];


Sakri