The mcu clock does not have to be a multiple of 3.58MHz in order to communicate at 9600baud. However, it it is, you can use the mcu oscillator as the source for the smartcard clock.

9600 baud * 372 = 3.58MHz thus the *magic* 372

So if you use a different clock frequency for the smartcard, then use this magic number to calculate the baudrate the smartcard will expect. baud rate = Clk freq/372

It seems you can run a separate oscillator for the smartcard.

As for wiring the TX & RX together depends on the actual mcu you're using. When the smartcard is sending data, you don't the the TX pin to be driving, on some mcus you can disable the transmitter thus solving your problem or use a mux as you suggest or at a pinch use a resistor in series with the TX pin. Something like 1k might be a start - read the smartcard specs to see how much current it can sink.


I think it might be worth your while to purchase the article I referred to. I dare say it will answer a lot of your questions and maybe save some time.