EM357-RTR datasheet(173/241 Pages) SILABS

173 / 241 page

173

Rev 1.3

10.1. Setup and Configuration

To use the ADC follow this procedure, described in more detail in the next sections:



Configure any GPIO pins to be used by the ADC in analog mode.



Configure the voltage reference (internal or external).



Set the offset and gain values.



If using DMA, reset the ADC DMA, define the DMA buffer, and start the DMA in the proper transfer mode.



If interrupts will be used, configure the top-level and second-level ADC interrupt bits.



Write the ADC configuration register to define the inputs, sample time, and start the conversions.

10.1.1. GPIO Usage

A GPIO pin used by the ADC as an input or voltage reference must be configured in analog mode by writing 0 to its

4-bit field in the proper GPIO_PxCFGH/L register. Note that a GPIO pin in analog mode cannot be used for any

digital functions, and GPIO_PxIN always reads it as 1. Only certain pins can be configured in analog mode. These

are listed in Table 10.1.

See "7. GPIO (General Purpose Input/Output)" on page 50 for more information about how to configure GPIO.

10.1.2. Voltage Reference

The ADC voltage reference (VREF), may be internally generated or externally sourced from PB0. If internally

generated, it may optionally be output on PB0. To output the internal VREF on PB0, the ADC must be enabled

(ADC_ENABLE bit set in the ADC_CFG register) and PB0 must be configured in analog mode.

To use an external reference, the Ember software must be called after reset and after waking from deep sleep. PB0

must also be configured in analog mode using GPIO_PBCFGH[3:0]. See the Ember software documentation for

more information on using an external reference.

Table 10.1. ADC GPIO Pin Usage

Analog Signal

GPIO

Configuration control

ADC0 input

PB5

GPIO_PBCFGH[7:4]

ADC1 input

PB6

GPIO_PBCFGH[11:8]

ADC2 input

PB7

GPIO_PBCFGH[15:12]

ADC3 input

PC1

GPIO_PCCFGL[7:4]

ADC4 input

PA4

GPIO_PACFGH[3:0]

ADC5 input

PA5

GPIO_PACFGH[7:4]

VREF input or output

PB0

GPIO_PBCFGL[3:0]

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