LPC15xx - Pull-up disable when configured as ADC

[jonathon_generac]

From LPC15xx device user manual (UM10736):

From Section 7.4.5:

When using a pin in analog mode, disable the pull-up and pull-down resistors.

From Section 7.5.1

If any of the pins is connected to an analog function through the switch matrix
PINENABLE registers, the digital portion of the pin is disconnected.

These two statements appear to contradict each other.

Do the pull-up resistors remain connected when the pin is configured as an ADC pin?  If not, please confirm that the pull-up resistor need not be disabled, as suggested above, when configuring as an ADC.

Thanks,

Jonathon

[xiangjun_rong]

Hi, Jonathon,

Regarding your question, pls refer to section 7.4.1 pin configuration in UM10736.pdf, you can see that the week pull-up and pull-down circuit is an independent circuit, belongs to IOCON module, you have to disable the both weak pull-up and pull-down so that the ADC sample is not effected by the pull-up and pull-down circuit.

Hope it can help you

BR

XiangJun Rong