LPC176x errata

[mikaelstolt]

I see in the errata for LPC176x that it is impossible to set a pin to open drain-mode unless it set as GPIO. How does that work if the pin is set to I2C mode?

[jeremyzhou]

Hi,

I've attached the I2C pins initialization function, please refer to it.

/* Sets up board specific I2C interface */
void Board_I2C_Init(I2C_ID_T id)
{
    switch (id) {
    case I2C0:
        Chip_IOCON_PinMux(LPC_IOCON, 0, 27, IOCON_MODE_INACT, IOCON_FUNC1);
        Chip_IOCON_PinMux(LPC_IOCON, 0, 28, IOCON_MODE_INACT, IOCON_FUNC1);
        Chip_IOCON_SetI2CPad(LPC_IOCON, I2CPADCFG_STD_MODE);
        break;

    case I2C1:
        Chip_IOCON_PinMux(LPC_IOCON, 0, 19, IOCON_MODE_INACT, IOCON_FUNC2);
        Chip_IOCON_PinMux(LPC_IOCON, 0, 20, IOCON_MODE_INACT, IOCON_FUNC2);
        Chip_IOCON_EnableOD(LPC_IOCON, 0, 19);
        Chip_IOCON_EnableOD(LPC_IOCON, 0, 20);
        break;

    case I2C2:
        Chip_IOCON_PinMux(LPC_IOCON, 0, 10, IOCON_MODE_INACT, IOCON_FUNC2);
        Chip_IOCON_PinMux(LPC_IOCON, 0, 11, IOCON_MODE_INACT, IOCON_FUNC2);
        Chip_IOCON_EnableOD(LPC_IOCON, 0, 10);
        Chip_IOCON_EnableOD(LPC_IOCON, 0, 11);
        break;
    }
}

Have a great day,
Ping

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[mikaelstolt]

Hi Ping,

thank's for the example but it did not really answer my question.

In your code you set the I2C-pins in open drain mode (Chip_IOCON_EnableOD(LPC_IOCON, 0, 11)

but according to the errata this is not possible if the pin is not used as a GPIO. So the question is, will it automatically be an OD when used as I2C. Otherwise there might be problems.

However, I can use the I2C interface without problem, but I would still know what gives in this case and any other setup of functions.

[rolfmeeser · Accepted solution]

Although the user manual states otherwise, setting the pin to open-drain mode manually in PINMODE_ODx is not required for I2C functions. As soon as you select one of SDA1, SCL1, SDA2, SCL2 for a pin in PINSELx, the corresponding output stage is forced into open-drain mode.

This is why the GPIO.1 erratum doesn't affect you when using I2C1 and I2C2.

[mikaelstolt]

Thank you Rolf.

Just want I wanted to hear!

Regards

Mike