i want to use two serial port of ds89c450 and use them at different baud rates one at 9600 and other at 4800. how should i do it. as there is only on TH1 and TL1 do i have to load different values corresponding to 2 baud rates. i want to use them parallely. do i have to initialize TH1 and TL1 each time i want to change the baud rate. how can i proceed.
If you need different baud rates, you will have to use separate timers
If, as you have written, one of your baudrates is half the other, then locate in the controllers data sheet the section describing smod_0 in the pcon register or smod_1 in the wdcon register.
SMOD would affect both baudrates, thus only useable if the two UARTs are never to run concurrently. If they are to run concurrently the only solution is one on T1 and one on T2.
Erik