NXP Semiconductors LPC84x, Руководство пользователя

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UM11029 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2017. All rights reserved.
User manual Rev. 1.0 — 16 June 2017 442 of 515
NXP Semiconductors
UM11029
Chapter 26: LPC84x 12-bit Analog-to-Digital Converter (ADC)
The VREFP and VREFN pins provide a positive and negative reference voltage input. The
result of the conversion is (4095 x input voltage VIN)/(VREFP - VREFN). The result of an
input voltage below VREFN is 0, and the result of an input voltage above VREFP is 4095
(0xFFF).
When the ADC is not used, tie VREFP to VDD and VREFP to V
SS
.
Remark:
For best performance, select VREFP and VREFN at the same voltage levels as
V
DD
and V
SS
. When selecting VREFP and VREFN different from VDD and VSS, ensure
that the voltage midpoints are the same:
(VREFP-VREFN)/2 + VREFN = V
DD
/2
26.4.1 ADC vs. digital receiver
The ADC function must be selected via the switch matrix registers in order to get accurate
voltage readings on the monitored pin. The MODE bits in the IOCON register should also
disable both pull-up and pull-down resistors. For a pin hosting an ADC input, it is not
possible to have a have a digital function selected and yet get valid ADC readings. An
inside circuit disconnects ADC hardware from the associated pin whenever a digital
function is selected on that pin.
Table 440. ADC supply and reference voltage pins
Function Description
V
REFP
Positive voltage reference. The VREFP voltage level must be between 2.4
V and V
DDA
. For best performance, select VREFP = V
DDA
and VREFN =
V
SSA
.
V
REFN
Negative voltage reference.
V
DDA
= V
DD
The analog supply voltage is internally connected to V
DD
.
V
SSA
= V
SS
ADC ground is internally connected to VSS.
Table 441. ADC pin description
Function Direction Type Connect to Use register Reference Description
ADC_0 AI external to pin PIO0_7 PINENABLE0 Table 195 Analog input channel 0.
ADC_1 AI external to pin PIO0_6 PINENABLE0 Table 195 Analog input channel 1.
ADC_2 AI external to pin PIO0_14 PINENABLE0 Table 195 Analog input channel 2.
ADC_3 AI external to pin PIO0_23 PINENABLE0 Table 195 Analog input channel 3.
ADC_4 AI external to pin PIO0_22 PINENABLE0 Table 195 Analog input channel 4.
ADC_5 AI external to pin PIO0_21 PINENABLE0 Table 195 Analog input channel 5.
ADC_6 AI external to pin PIO0_20 PINENABLE0 Table 195 Analog input channel 6.
ADC_7 AI external to pin PIO0_19 PINENABLE0 Table 195 Analog input channel 7.
ADC_8 AI external to pin PIO0_18 PINENABLE0 Table 195 Analog input channel 8.
ADC_9 AI external to pin PIO0_17 PINENABLE0 Table 195 Analog input channel 9.
ADC_10 AI external to pin PIO0_13 PINENABLE0 Table 195 Analog input channel 10.
ADC_11 AI external to pin PIO0_4 PINENABLE0 Table 195 Analog input channel 11.