may be I have not understood the precise problem, so let me clarify what I propose. The mode0 is basically the shift register mode of serial comm, that is the Tx pin emits the clock which is a ratio of the system clock. Conversely if I PLL(& multiply) the ext clock of 32kHz and use it in place of the 8052 clock then I am synchronized to the ext clk. Actually this would be true for all modes of serial comm.