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SCI COMMUNICATION BETWEEN ST7 AND PC

2 RS232 COMMUNICATION WITH A PC

2.1 MAIN FEATURES

The electrical and protocol characteristics of RS232 are different from those of the ST7 SCI

peripheral. In RS232 communication, high level is typically +7V and low level is typically -7V,

while the SCI peripheral works with TTL levels (0, +5V).

Furthermore, the polarities are different. A ’1’ bit coming from the SCI corresponds to a ’0’ bit

in RS232, and a ’0’ bit to a ’1’ bit. It is true for all bits including the start and stop bit.

So it is necessary to implement a conversion between the PC and the SCI peripheral. In this

application a MAX232 is used for this purpose.

2.2 PC CONFIGURATION

The PC will be used as a terminal. The description below refers to the Windows 98 environ-

ment. This terminal application is called hyperterminal.

Under Windows, open the «hyperterminal» application. To configure it, go to the communica-

tion parameters menu. The options of this window must be the same as the ones defined with

your ST7.

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

figured in the micro. As the PC accepts only one baud rate, transmission and reception baud

rates will have the same value. 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 ST72F264.ht file is also pro-

vided in the corresponding zip file).

The PC is then correctly configured.