Functional software flow

AN1753

12/22

DocID9986 Rev 2

6

Functional software flow

The character format used is “ASCII”. Before starting a communication, you should

configure the communication parameters to your requirements. You can select the baud

rate, number of bits and stop bits in different combinations. However, for a correct

communication, the receiver must have a reception baud rate strictly equal to the

transmission baud rate of the transmitter. If not, the communication will be corrupted. So you

have to configure the “Hyperterminal” correctly.

To configure the device, you must set del_1bh, del_1bl, del_sampl, del_samph, STOP_BIT

and TxRx_data_lnth correctly in your software.

After power on, the ST7FLITE0 goes to transmit mode. It initiates the communication by

transmitting character “$” in ASCII format and then goes to receive mode. The PC then

receives this character on its serial port, which can be viewed in the Hyperterminal window.

You then have to press a key (character) to transmit. After pressing a character key, it gets

transmitted and the ST7LITE0 receives it. The ST7LITE0 then sends the same received

character to the PC. This sequence can be repeated continuously (see Figure 5).

6.1

Main software routines

The UART software consists of 4 main routines:

•

Tx_data

•

Rx_data

•

EI1_Interrupt

•

OPCOMP_int

Tx_data: This routine is used to transmit data in bit format stored in variable “TX_byte”. It

also takes care of the synchronization and of the output compare interrupt. The AT timer is

initialized to the application configuration inside this routine.

Rx_data: This routine is used to receive data on the input pin in bit format and stores it in

“RX_byte”. To detect a start bit, it initializes the PA7 pin in interrupt mode.

EI1_Interrupt: This “ei1” interrupt routine gets executed only once during receive data when

PA7 receives a start (high to low edge) bit. It also initiates the AT timer for a half bit duration.

OPCOMP_int: This routine gets executed in both transmit and receive modes. During a

Tx_dataroutine execution, it gets executed for each data bit transfer. It is actually used to

transmit data on the TxD (PA3) pin along with the start and stop bits.

In receive mode, it gets executed for each data bit received, including the start and stop bits.

The majority-voting system is implemented in the same section of code.