# A/D Convertor
* [ADC - 成大資工 wiki](http://wiki.csie.ncku.edu.tw/embedded/ADC#introduction-to-adc)
* VREF+ / VREF-
> e.g. VREF- = 0V, VREF+ = 10V
> 10 bit resolution -> range = [0, 1023]
> 0V -> 0
> 5V -> 511
> 10V -> 1023

## A/D conversion clock
* $T_{AD}$ (A/D Conversion time per bit)
* $T_{AD}$ 愈小愈好，但是要大於最小 $T_{AD}$



假設今天的頻率 ($F_{OSC}$) 是 2.86 MHz, 則周期 ($T_{OSC}$)會是 $\frac{1}{2.86 \times 10^6} \approx 0.35\mu s$，為了滿足最低 A/D Clock period ($0.7 \mu s$), 我們要把 conversion clock ($T_{AD}$) 設成兩倍的 $T_{OSC}$

## Acquisition time



## Left/Right justified
[Source](https://techetrx.com/pic-microcontroller/adc-in-pic16f887-microcontroller/)

## ADC Module

### Input
* AN0~AN12
> Note: 使用 ADC 的同時若發現其他 PORT 的 input 值怪怪的也許是誤把那些 PORT 設成 analog input (參考 ADCON1)

### ADRES
### ADCON0

## ADCON1

## ADCON2

## Workflow
1. Configure the A/D module:
* Configure analog pins, voltage reference and digital I/O (ADCON1)
* Select A/D input channel (ADCON0)
* Select A/D acquisition time (ADCON2)
* Select A/D conversion clock (ADCON2)
* Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if desired):
* Clear ADIF bit
* Set ADIE bit
* Set GIE bit
3. Wait the required acquisition time (if required).
4. Start conversion, set GO/DONE bit (ADCON0 register)
> 如果使用 CCP2 的 special event trigger 則不用手動設置 GO/DONE bit
5. Wait for A/D conversion to complete
(Wait for the A/D interrupt)
6. Read A/D Result registers (ADRESH:ADRESL);
clear bit, ADIF, if required.
7. For next conversion, go to step 1 or step 2, as required. The A/D conversion time per bit is defined as TAD. A minimum wait of 2 TAD is required before the next acquisition starts.

## CCP2 Module
* CCP2M3:CCP2M0 -> 1011 (CCP2CON<3:0>)
* Timer1 or Timer3 counter

## Variable resistor
左右一邊接 5V，一邊接地，中間接輸入