Dixon,

Most "serial devices" arent' the tye you hook up to TXD & RXD. Its a simple clocked bus most like SPI (see a recent message on that topic).

Unless you have a unique temperature sensor IC that requires RS232, then all you require is two port pins, one for data, another fo clock. You may need a third for chip enable depending upon your use of the sensor.

Often SPI type interfaces allow you to use the DAT and CLK signals to many serial devices. The device actively using the line is the one enabled.

Its also possible that you have a "I2C" interface which is slightly more difficult. It uses merely two lines but has a protocol that address different types of I2C chips. Their most often application is as EEProm and RTC chips.

If you have a real serial communications interface with a sensor IC (more likely if it were an external module), than you can use a 74'4052 to mux the RX and TX devices among 4 such ports.

If you have further questions I'd recommend postin the IC product number.

-Jay C. Box