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TM4C1294NCPDT: Flow control of UART3 for TM4C1294

Part Number: TM4C1294NCPDT

Hi,

Let me talk about Flow control of UART for TM4C1294.

My cusotmer develop an RS232C communication device using UART 3 peripheral of TM4C1294.

Hard flow control by RTS/CTS is decribed in Datasheet of TM4C1294.
and We set the receive side is set to Low of RTS signal by receiving 1 byte.

However, the transmission of TM4C does not stop and transmission of 2 bytes is also occurring,
if it operates at 300 kbps or higher, even when UnCTS of TM4C1294 falls to LOW due to 1 Byte received,

I have a few questions.

(1)
Will it continue to be transmitted,
even if the transmission is disabled by hardware flow control(CTS is Low)?
if yes, how to control for flow data when it is over 300 kbps or higher ?

(2)
In 250kbps case, it seems to be necessary to disable Tx output due to UnCTS fluctuation,
We see this time is 3.5us,
Is this correct ??
The timing chart of UART is not found on TM4C datasheet.

Best Regards
Hiroyasu

  • The Request To Send (RTS) must be deasserted at least one bit timing before the start bit of the next character. If you are using only one stop bit, that means the receiving device must deassert RTS before it has finished receiving the previous character.

    I am sorry, I do not understand your second question. Would you please rephrase it and ask again?
  • Hi Hiroyasu-san,
    Some questions:
    1. Do you have a pictorial diagram of your setup? How are you connecting between the MCU and the receiving device? Just wanted to make sure the RTS from the MCU is connected to the CTS of the receiving device and vice versa.
    2. How deep is your receiving device RX FIFO? Or does the receiving device have a FIFO at all?
    3. Do you know At what baud rate is the flow control working?
    4. Is the MCU in FIFO mode? What if you disable the FIFO mode, will it make a difference/

    What I'm suspecting is that the RTS from the receiving device is sent while the MCU has prepared to send the second byte and it is not able to halt it since the transmission has already started.
  • Hi, Bob-san, Charles-san

    Thank you for your reply,
    Your answers are enough.
    Thank you so much.

    Best Regards
    Hiroyasu