Real time plotting in Matlab

Hey ppl need some help, im working on a temperature controller that is based on 89c52 microcontroller, the sensor data is conv to digital by an adc0804 & the data is sent to the pc via the rs232 port, i need to plot a temp graph using matlab in real time, ive read that the hold function could be used but i havent had any success so far........ need help with the matlab code, the rest is fine... the baud rate is 9600