UART3 won't send data

vance · ‎2014-07-29

Posted on July 29, 2014 at 21:28

I'm using UART3 for RS-485 communications (I have a B&B RS-232 to RS-485 converter connected between the PC and the board). The trouble is that the UART3 won't ''send'' the data unless I put a debug break-point shortly after sending data via UART3. The data then sends fine. Without the break-point, the PC doesn't receive the data. Here is my function for sending data:

void send_485(uint8_t *ptr, uint8_t length)

{

uint8_t i = 0;

uint8_t count = _1s_counter;

GPIO_WriteHigh(GPIOE, GPIO_PIN_4);

while(_1s_counter < count+5){}

while (length-- > 0)

{

/* Wait while UART3 TXE = 0 */

while (UART3_GetFlagStatus(UART1_FLAG_TXE) == RESET)

{

}

UART3_SendData8((ptr[i++]));

}

count = _1s_counter;

while (UART3_GetFlagStatus(UART1_FLAG_TXE) == RESET)

{

}

while(_1s_counter < count + 1000){}

GPIO_WriteLow(GPIOE, GPIO_PIN_4); // Put break-point on this line.

}

Any ideas as to what the debugger does that makes the communication work? Adding that break-point, the bytes are received flawlessly.

Thanks,

Vance

#uart3 #rs485 #stm8

kirill · ‎2014-08-01

Posted on August 01, 2014 at 16:57

Hi, Vance.

Your code looks a little bit redundant, as for me. Here's the code I use to send consequence of bytes via RS485 using STM8 MCU:

#include <iostm8s003f3.h>

#define TX_ENABLE PD_ODR_ODR4

void RS485_send_packet(unsigned char *packet, int len)

{

UART1_CR2_RIEN = 0; // Disable receive interrupt

TX_ENABLE = 1;

while (len)

{

UART1_DR = *packet; // Put the next character into the data transmission register.

while (UART1_SR_TXE == 0); // Wait for transmission to complete.

packet++; // Grab the next character.

len--;

}

while (!UART1_SR_TC); // Wait for transmission of the last byte to complete

UART1_CR2_RIEN = 1; // Enable receive interrupt

TX_ENABLE = 0;

}

It works fine.

P.S.: I don't remember, why I disable receive interrupt before start of transmission... Probably had some issues with that.