LPCXpresso55S69 EVK, LPADC "A0"

[richardkrehbiel]

I have the NXP LPCXpresso55S69 EVK (Rev A1), and SDK 2.6.3.  I import the example "lpcxpresso55s69_lpadc_interrupt."

I read in the board schematic that the Arduino A0 is tied to pin 14, PIO0_16.  So I change the .MEX and this generates a mapping as such:

const uint32_t port0_pin16_config = (
IOCON_PIO_FUNC0 | /* Pin is configured as ADC0_8 */
IOCON_PIO_MODE_INACT | /* No addition pin function */
IOCON_PIO_SLEW_STANDARD | /* Standard mode, output slew rate control is enabled */
IOCON_PIO_INV_DI | /* Input function is not inverted */
IOCON_PIO_ANALOG_EN | /* Enables analog function */
IOCON_PIO_OPENDRAIN_DI | /* Open drain is disabled */
IOCON_PIO_ASW_DIS_EN); /* Analog switch is enabled */

/* PORT0 PIN16 (coords: 14) is configured as ADC0_8 */
IOCON_PinMuxSet(IOCON, 0U, 16U, port0_pin16_config);

I change the following line of the source file lpcadc_interrupt.c:

#define DEMO_LPADC_USER_CHANNEL 8U

I can build and run this.  However, the ADC always reads the value 1, whether I jump A0 to 3v3 or to ground.

Help?  Thanks.

[richardkrehbiel]

I've now heard that the PIO-to-channel mapping listed in the User Manual is wrong; subtract 8 from all of the channel numbers for all of the B-side ADC channels.

In fact, when I map the pin as Side B Channel 0, I get readings I expect (4095 for 3v3, 0 for Gnd).

[FelipeGarcia]

Hello Richard,

That table in the UM is incorrect. It should be like this:

Function	Connection	Description
ADC0_4	PIO1_8	A-side mux, analog input channel 4.
ADC0_3	PIO0_31	A-side mux, analog input channel 3.
ADC0_2	PIO0_15	A-side mux, analog input channel 2.
ADC0_1	PIO0_10	A-side mux, analog input channel 1.
ADC0_0	PIO0_23	A-side mux, analog input channel 0.
ADC0_12	PIO1_9	B-side mux, analog input channel 4.
ADC0_11	PIO1_0	B-side mux, analog input channel 3.
ADC0_10	PIO0_12	B-side mux, analog input channel 2.
ADC0_9	PIO0_11	B-side mux, analog input channel 1.
ADC0_8	PIO0_16	B-side mux, analog input channel 0.

Best regards,

Felipe

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