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STR71x UART COMMUNICATION WITH A PC USING RS232

2 RS232 COMMUNICATION WITH A PC

2.1 MAIN FEATURES

The electrical and protocol characteristics of the STR71x UART peripheral are different from

RS232. In RS232 communication, high level is typically +12 V and low level is typically -12 V,

while the UART peripheral works with TTL level (0, +5V).

The adaptation is done using a line adapter circuit (ex: ST3232), which transforms the logic

levels output by the digital system into RS232-compatible levels and vice versa.

2.2 PC CONFIGURATION

In this example, the PC will act as a terminal. The description below refers to the Windows en-

vironment. The Windows terminal application is called HyperTerminal.

Under Windows, open the “HyperTerminal” application. To configure it, go to the communica-

tion parameters menu. The options that you set in this menu must be the same as the ones

defined in your STR71x.

After selecting the right serial communication port, select the same baud rate as the one con-

figured in the microcontroller. Data word length will be 8 bits, but you can choose to use 1 or

2 stop bits. “Flow control” can be either Xon/Xoff or none.

The PC is then correctly configured.

2.3 GENERAL INITIALIZATION

The external clock works at 16 MHz.

In the STR71x, four UARTs are available. In this application only UART0 is used. Two pins of

the STR71x are used:

- the TX0 pin (Transmit Data Output, alternate function of P0.9).

- the RX0 pin (Receive Data Input, Input Tristate CMOS of P0.8).

The value of the Port 0 Data Register does not matter.