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UART on a 3S2965

Prodigy 210 points

Replies: 2

Views: 1274

Is there a weak pullup on a pin when it is configured as a UART Rx? I am trying to interface a Parallax GPS module that uses 5V logic on a single pin asynchronous serial line. I have connected the GPS line to the Rx pin on the 3S2965 through a 15k resistor and I find that the resistor doesn't pull the line down very much, 0.4V or so.

2 Replies

  • The GPIOPinTypeUART function configures the pin to be a standard push/pull pin with no pullup or pull down.
    Regards,
    Sue
  • That is peculiar, I thought the Rx pin on a UART was always high-Z.

    Update.

    I found that following code does indeed configure the UART Rx pin as an input pin that requirs an external 10k pull-up resistor to hold the line at 3.3V:

    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART2); // Enable the UART 2 peripheral.
    IntMasterEnable();
    GPIOPinTypeUART(GPIO_PORTG_BASE, GPIO_PIN_0 | GPIO_PIN_1);
    UARTConfigSetExpClk(UART2_BASE, // UART is 4800 baud, 8 bits,
    SysCtlClockGet(), // 1 stop, no parity.
    4800,
    UART_CONFIG_WLEN_8 |
    UART_CONFIG_STOP_ONE |
    UART_CONFIG_PAR_NONE);
    IntEnable(INT_UART2);
    UARTIntEnable(UART2_BASE, UART_INT_RX | UART_INT_RT);

    The input looks like a high-Z to me, just as it should be. The term push-pull does not appear in the LM3S2965 datasheet, so I guess I don't know what that means in the source code description. A more detailed diagram of the UART would be helpful. Something that ties in with the Figure 9-1 GPIO Port Block Diagram would be nice.

    Post edited by: edplambeck@att.net, at: 2009/10/05 22:23

    Post edited by: edplambeck@att.net, at: 2009/10/05 22:25

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