topic UART on I2C pins in LPC Microcontrollers

UART on I2C pins

sanders7284 — Thu, 05 Apr 2018 12:35:43 GMT

Hello, is it possible to use a UART on the I2C pins?

I have tried the following but the functionality seems to be intermittent.

void UART_INIT(void) //---------------------------------------------------------
{

//Connect the U0_TXD_O and not used U0_RXD_I signals to port pins(P0.10, not used P0.11)
Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_SWM); // Enable SWM clock before altering SWM
Chip_SWM_DisableFixedPin(SWM_FIXED_I2C0_SDA);
Chip_SWM_DisableFixedPin(SWM_FIXED_I2C0_SCL);
Chip_SWM_MovablePinAssign(SWM_U0_TXD_O, 10);
Chip_SWM_MovablePinAssign(SWM_U0_RXD_I, 11);
Chip_Clock_DisablePeriphClock(SYSCTL_CLOCK_SWM); // Disable SWM clock after altering SWM

Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_UART0);
Chip_UART_Init(LPC_USART0);
Chip_UART_ConfigData(LPC_USART0, UART_CFG_ENABLE | UART_CFG_DATALEN_8 | UART_CFG_PARITY_NONE | UART_CFG_STOPLEN_1);
Chip_Clock_SetUSARTNBaseClockRate((BAUD_RATE * 16), true);
Chip_UART_SetBaud(LPC_USART0, BAUD_RATE);
Chip_UART_Enable(LPC_USART0);

Chip_UART_IntEnable(LPC_USART0, UART_INTEN_RXRDY);
Chip_UART_IntDisable(LPC_USART0, UART_INTEN_TXRDY); /* May not be needed */
NVIC_EnableIRQ(UART0_IRQn);
}
//------------------------------------------------------------------------------

// UART0_IRQ -------------------------------------------------------------------
void UART0_IRQHandler(void)
{

   NVIC_ClearPendingIRQ(UART0_IRQn);
    Rx_State[s] = Chip_UART_ReadByte(LPC_USART0);

    if (Rx_State[s] != Last_Rx_State)
    {

    switch (Rx_State[s])
    {
    case 1: //Normal
      New_Event(1);
      break;

    case 2: //off
    case 3: //off
    case 4: /off
      New_Event(2);
      break;

    case 5: //Fault
      New_Event(3);
      break;

    case 6: //test 1
      New_Event(4);
      break;

    case 7: //test 2
      New_Event(5);
      break;

    case 8: //learn
      break;
    }

    }

    Last_Rx_State = Rx_State[s];
    s ++;

    if (s >= 16)
    {
      s = 0;
    }
}

Re: UART on I2C pins

victorjimenez — Thu, 05 Apr 2018 17:04:31 GMT

Hello Paul,

Could you please provide more information. Which LPC are you using? Are you using an evaluation board? The pins you are using are P0_10 and P0_11, right?

Regards,

Victor.

Re: UART on I2C pins

sanders7284 — Fri, 06 Apr 2018 07:35:34 GMT

Thanks Victor,

The uC is a LPC824,

I am using p0_10 & p0_11,

The PCB is custom but basically each line has an external pull up and an connection to a header pin.

Regards Paul

Re: UART on I2C pins

victorjimenez — Fri, 06 Apr 2018 17:03:19 GMT

Hello Paul,

I used an example of the CodeBundle for the LPC824 (Example_UART0_Terminal) At first the example uses the P0_0 and P0_4 for the UART0, I made the changes to use P0_10 and P0_11 and I connected these two pins to an external pull up of 4.7K. The example worked as expected even with the pin change. I also tried with different baudrates (2400, 9600 and 115200) and everything went well.

You can use this example as a guide to see how configurations are made and see if you are missing something. The example is really good commented so it easy to understand how it works.

The changes I made in the example project are the next ones.

First I activate the desired pins:

  // Connect UART0 TXD, RXD signals to port pins
  ConfigSWM(U0_TXD, P0_10);       // Use with USB-to-RS232 break-out cable (see jpeg)
  ConfigSWM(U0_RXD, P0_11);       // Use with USB-to-RS232 break-out cable (see jpeg)
  //ConfigSWM(U0_TXD, TARGET_TX);  // For MBED serial port (requires board mod.)
  //ConfigSWM(U0_RXD, TARGET_RX);  // For MBED serial port (requires board mod.)
‍‍‍‍‍

Then I change the baudrate in the following line:

  // Configure the USART0 baud rate generator
  LPC_USART0->BRG = 781;‍‍

I obtain the value of BRG (depending on the desire baudrate) of the next equation:

  // BRG = ((MainClock Hz.) / (2 * 16 * baudrate Hz.)) - 1
  //     = (60,000,000/(2 * 16 * 115200)) - 1‍‍

Please let me know if you have more questions or doubts!

Victor.

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Re: UART on I2C pins

sanders7284 — Mon, 09 Apr 2018 06:35:30 GMT

Thanks Victor,

The problem seems to be with my pull up resistors.

I had 1k fitted given the I2C application, I changed these to 47k so it matched everything above and the code I already had jumped into life.

Regards Paul