UART TX buffer status is never empty even right after clearTXBuffer function is called?

[Anonymous]

Hi

I got a UART transmission block working, sending 4 bytes at a time but the logic i'm using is actuallly not making a lot of sense to me, even though it works.

I was checking if the transmission status was FIFO not full, but what really makes sense is to check if the FIFO is empty so I can immediatly load it with the 4 bytes to send. When I do this, however, it never goes into the if, it's always false even if right before checking it I place the clearTXBuffer and I don't understand why.

Does anyone have any idea? Am I understanding the functioning wrong? I've read the datasheet some 3 or 4 times and this is what I could understand from it.

Thanks.

[BragadeeshV]

Hi Pedro,

Could you please share your project file or code snippet focusing on your question? Also mention the device you're using.

Regards,

Bragadeesh

[Anonymous]

Hi Bragadeesh

Here is the infinite loop snippet with the function:

for(;;) 
    { 
        temp_read=read_temperature(); // returns a float with the temperature
        voltage_read = convert_current();
        //current = (voltage_read-2.5)/current_sensitivity;
        real_voltage=convert_voltage();
        if(temp_read != -1000){ //reading of temp was correct
            memcpy(&tempFloatToArray, &temp_read, sizeof(tempFloatToArray)); //transforms the float into a char array with 4 bytes
            if(UART_1_ReadTxStatus() != UART_1_TX_STS_FIFO_FULL){ //if(UART_1_ReadTxStatus() != UART_1_TX_STS_FIFO_NOT_FULL){
                for(j=0;j<sizeof(tempFloatToArray);j++){
                UART_1_WriteTxData(tempFloatToArray);
                }
            }
        clear_dataBuf();
        }
        CyDelay(125u);
}

What I'm talking about is line 12. It works if I do it like it is in the snippet, but it doesnt if I do

if(UART_1_ReadTxStatus == UART_1_TX_STS_EMPTY){

...

}

I just don't understand why. How does it put the 4 bytes of data I have in the 4 byte tx buffer if it's not even empty? I mean it works, it's just that I need to comment and justify the code I developed and I'm honestly not understanding why it even works at all.

Thanks

[Bob_Marlowe · Accepted solution]

UART_1_ReadTxStatus() returns a bit pattern indicating different states that have happened (see datasheet of the UART you are using).

Try

if(UART_1_ReadTxStatus & UART_1_TX_STS_EMPTY){

...

}

which will be true when the EMPTY bit is set.

Bob

[Anonymous]

Thanks Bob, it works when I use the '&' logic operator like you posted it works fine, but I was doing it like this:

if(UART_1_ReadTxStatus == UART_1_TX_STS_EMPTY){

...

}

Which didn't work, i'm assuming because of the way the uart component checks and provides the buffer status.

Thanks for the help once again!