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Using the printf Function in PSoC® 3 - KBA83472

Last Updated: 01/08/2013
Version: *A
Question: How do I use the printf function in stdio.h to send data to UART?

Answer: Keil’s printf function calls the putchar() to send characters but the default putchar uses an UART based on the Special Function Register (SFR), which PSoC® 3 does not have. Therefore, to use printf, the program must override Keil's built-in putchar function.

For example, if ‘UART’ is the instance name of the UART component in your project, then write the following function in the main.c file to override Keil’s built-in putchar function:

char putchar(char c)
{
UART_WriteTxData((uint8)c);
return c;
}

Then, printf can be used to send data to UART in the following manner (note that the putchar() function should either be defined or declared before the first call to the printf() function for proper execution):

void main() {
UART_Start();
while (1) {
printf("Hello world"); // uses the new putchar() function to stream data to the UART
while(!(UART_ReadTxStatus() & UART_TX_STS_COMPLETE)); // wait until transfer is complete
}
}

Related Categories: PSoC® 3



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Sunset Owner: KUMR; Secondary Owner: KUMR; Sunset Date: 05/23/13