LPC932 EXAMPLE: COMMUNICATION WITH THE PC USING THE SERIAL INTERFACE (UART)
Christian Kulig, 12/05/02
INTRODUCTION:
The LPC932 has an enhanced UART which is compatible with the conventional 80C51 UART.
It can be used directly as a serial interface to exchange data with other microcontrollers.
To communicate with a PC it is necessary to adapt the voltage levels from 0V and 3.3V
(CMOS levels of LPC900 UART) to -10V and +10V (RS232 specification of PC com-port).
There are several IC's which are suitable for this task, e.g. the MAX232 or the LTC1386.
These devices are supplied with 3.3V or 5V and have a on-chip charge pump for providing the +/-10V.
Please notice, that the Keil EPM900 Board does not include these devices, therefore this example can't be
tested directly with the EPM900.
To transfer data, the UART uses a certain baud rate (bits per second), which must be the same for the
transmitter and the receiver. For PCs there are standard baud rates like 1200, 4800, 9600 and so on,
which should be used for the UART of the microcontroller as well.
On the LPC932 the source for the baud rate can be e.g. the Timer 1 overflow or the independent
Baud Rate Generator (BRG). Both divide the clock frequency (Crystal, internal RC oscillator) by a certain
factor, so that many different baud rates can be achieved.
DESCRIPTION:
This example shows how to use the UART to communicate with a PC:
It sets up the 8 data bits mode with 1 stop bit and no parity bit. The baud rate source is the internal
Baud Rate Generator, which is set up to provide a baud rate of 9600 at an oscillator frequency of
12 MHz (=external resonator).
To have access to the com port of the PC, start the program 'Hyperterminal'.
(START -> PROGRAMS -> ACCESSOIRES -> COMMUNICATIONS -> HYPERTERMINAL)
Click on 'Properties' and check the following settings: 9600 baud, 8 data bits, 1 stop bit and no flow control.
To begin the communication click on 'Call'.
The LPC932 waits for a command ('S'), which is sent by 'Hyperterminal' and sends
back a response which is displayed on the screen.
