EM357-RTR datasheet(177/240 Pages) ETC2

177 / 240 page

EM351 / EM357

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

Write the ADC configuration register to define the inputs, voltage range, 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.

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]

See Chapter 7, GPIO 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.

10.1.3 Offset/Gain Correction

When a conversion is complete, the 16-bit converted data is processed in several steps by offset/gain

correction hardware:

1. The initial signed ADC conversion result is added to the 16-bit signed (two’s complement) value of the ADC

offset register (ADC_OFFSET).

2. The offset-corrected data is multiplied by the 16-bit ADC gain register, ADC_GAIN, to produce a 16-bit

signed result. If the product is greater than 0x7FFF (32767), or less than 0x8000 (-32768), it is limited to

that value and the INT_ADCSAT bit is set in the INT_ADCFLAG register.

3. The offset/gain corrected value is divided by two to produce the final result.

ADC_GAIN is an unsigned scaled 16-bit value: ADC_GAIN[15] is the integer part of the gain factor and

ADC_GAIN[14:0] is the fractional part. As a result, ADC_GAIN values can represent gain factors from 0 through

(2 – 2-15). Although ADC_GAIN can represent a much greater range, its purpose is to correct small gain error,

and in practice is loaded with values within a range of about 0.95 to 1.05.

10-2

120-035X-000D

Preliminary

EM357-RTR 数据表(PDF) 177 Page - List of Unclassifed Manufacturers

EM357-RTR 数据表(HTML) 177 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载