5 Replies Latest reply on Oct 23, 2014 12:43 PM by kristopher.young

    UART complete before continuing


       Is there a command that can send data but not continue until all data has been sent out UART?


      In my code below, the UART data is sent After the EN goes low again. I want to have 10ms of EN high, then send the data byte and then have EN low. However, the EN goes high and low and then data appears on port pin. I also tried WriteTXData function. Attached is copy of the component layout on workspace. The required output is 125 kHz carrier for 10ms followed by ASK modulated carrier. The enable pin controls external hardware and should enable the chip when carrier and data sent and then go low. Thanks








             EN_Write(1);  //Start Carrrier




             UART_PutChar(0x55);  //Send Modulated data









        • 1. Re: UART complete before continuing

          You can always use a LUT to create a state machine to


          sequence operations and check for completion, etc....








          http://www.cypress.com/?rID=44402     AN62510 - Implementing State Machines with PSoC® 3, PSoC 4, and PSoC 5LP


          http://www.cypress.com/?rID=52365     State machines using LUTs Video




          Regards, Dana.

          • 2. Re: UART complete before continuing

            You can use UART_ReadtxStatus() to check for an empty Tx FIFO.


            (Actually PutChar() is blocking, but in blocks only when the Tx FIFO is full, and its 4 bytes...)

            • 3. Re: UART complete before continuing

              you need to wait for BOTH fifo empty and transmit complete. the fifo can hold upto 4 bytes and the 'shift register' for output is a separate byte. so you have to have the fifo empty AND the last bit shifted out.




              uint8 UART_ReadTxStatus(void)
              Description: Reads the status register for the TX portion of the UART.
              Parameters: void
              Return Value: uint8: Contents of the TX Status register
              Value Description
              UART_TX_STS_COMPLETE If set, indicates byte was transmitted
              UART_TX_STS_FIFO_EMPTY If set, indicates the TX FIFO is empty
              UART_TX_STS_FIFO_FULL If set, indicates the TX FIFO is full
              UART_TX_STS_FIFO_NOT_FULL If set, indicates the FIFO is not full
              Side Effects: This function reads the TX status register, which is cleared on read.





              • 4. Re: UART complete before continuing

                 Here's some code that I used in a PSoC3 - should also work in a PSoC4. I set fUARTTransmitActive to TRUE whenever I transmit anything. SleepFunc() only gets called after everything is completely transmitted.






                /* Read our TX status byte to make sure we don't sleep when still transmitting data */
                bTXStatus = UART_1_ReadTxStatus(); /* Some of these bits clear on read, so just read once before checking! */


                /* Here we need to do some checking to make sure it is OK to go to sleep. We want to wait until any
                * serial transmit has been completed.
                * Here are the conditions that need to be satisfied:
                * 1. UART_1_GetTxBufferSize() == 0: We don't have any data in the transmit buffer which has not been loaded
                * into the UART FIFO.
                * 2. bTXStatus & UART_1_TX_STS_FIFO_EMPTY: The UART TX FIFO is empty
                * 3. !((fUARTTransmitActive == TRUE) && !(bTXStatus & UART_1_TX_STS_COMPLETE)) : If we didn't transmit this
                * wake cycle (fUARTTransmitActive == FALSE), we can safely go to sleep. If we did transmit this cycle and
                * TX complete is set (i.e. byte has completely transmitted), we can safely go to sleep. We cannot go to
                * sleep if we did transmit this cycle and TX complete is not set (i.e. byte has not completely transmitted).
                * NOTE that we can't just simply check TX complete, since it won't be set if we didn't transmit this cycle
                * (but it would be OK to go to sleep in that case).

                if ((UART_1_GetTxBufferSize() == 0 ) && (bTXStatus & UART_1_TX_STS_FIFO_EMPTY) && !((fUARTTransmitActive == TRUE) && !(bTXStatus & UART_1_TX_STS_COMPLETE)))
                fUARTTransmitActive = FALSE; /* Reset flag before sleep */

                • 5. Re: UART complete before continuing

                  If its really just about a single byte, checking the transmit state might be enough (because the byte is starting to be send as soon as it got put into the transmit buffer).