Lecture 25: Recap - A/D, Timer_A, and msp432_recorder_demo

10:10 A/D Main Points

Conversion Formula from analog to digital

                        Vin - Vref-
            D = floor{ ------------- . (2^n - 1) + 0.5 }
                       Vref+ - Vref-

Conversion Formula from digital to analog
                
                      D
            Vout = ------- . (Vref+ - Vref-) + Vref-
                   2^n - 1

SPAN               =  Vref+ - Vref-
ANALOG RESOLUTION  = (Vref+ - Vref-) / (2^n - 1)
DIGITAL RESOLUTION = n
				   
-> Chart

R-2R Ladder DAC

                I/2              I/4

    Vin --+----///R//-----+----///R//-----+---------------+
          |               |               |               |
          //              //              //              //
          2R  I/2         2R  I/4         2R  I/8         2R  I/8
          //              //              //              //
          |               |               |               |
          +               +               +               +
         / \             / \             / \             gnd
       b2-switch       b1-switch       b0-switch
        +   +           +   +           +   +  
       gnd  |           gnd |          gnd  |
            |               |               |
            +---------------+---------------+
                            | 
                            +-----+-----//R///---------+
                                  |                    |
                                  |     | \            |
                                  |     |  \           |
                                  +-----+ - \          |
                                        |    +---------+---- Vout
                             gnd -------+ + /
                                        |  /
                                        | /

A/D Conversion:
	- Sample and Hold
	- SAR Conversion
	
Sample and Hold

	exp (-tacq / (R.C)) < 1 / 2^n
            
    => tacq > n . (R.C) . ln(2)

SAR

   Try code 1000 -> decide 0000 or 1000
   Try code n100 -> decide n000 or n100
   Try code nn10 -> decide nn00 or nn10
   Try code nnn1 -> device nnn0 or nnn1
   done
   
	Repetitively apply DAC formula, and compare generated voltage
	to input voltage
	
	For n bit: conversion time = n * bit-conversion time
	
Total conversion time = Acquisition time + Conversion time

10:20 MSP432 ADC14 Block Diagram and Driverlib Function Calls

                            Conversion
                               Clock
    INPUT  0 -|\                 |      +-------+
    INPUT  1 -| \                V      | MEM0  |
    INPUT  2 -|  +---> S/H ---> SAR --->|  ...  |
    ...       | /       ^        ^      | MEM31 |
    INPUT 31 -|/        +---+----+      +-------+
                            |
            Analog Mux      |         Memory Buffer
                         Trigger

Configuration Procedure:

	1/ Choose conversion mode (single channel, multichannel)
	     - single channel/multi-channel
		 - repetitive/ not-repetive
		 
			ADC14_configureSingleSampleMode
			ADC14_configureMultiSequenceMode
	
	2/ Choose conversion clock
	
			ADC14_initModule
		
	3/ Choose sample timer (manual or auto-repeat)
	
			ADC14_enableSampleTimer
	
	4/ Map channels to buffer locations
	
			ADC14_configureConversionMemory
	
	5/ Configure GPIO ports to work as analog inputs

			GPIO_setAsPeripheralModuleFunctionInputPin
	
Making a conversion:

	0/ Enable Module
	
			ADC14_enableModule

	1/ Enable conversion
	
			ADC14_enableConversion
	
	2/ Trigger conversion
	
			ADC14_toggleConversionTrigger	
			
	3/ Wait until the ADC is done
	
			ADC14_isBusy
	
	4/ Read the result

			ADC14_getResult
	
Example of a continuous-conversion:

https://github.com/vt-ece2534-s18/msp432-adc-examples/blob/master/msp432-microphone-lcd/microphone.c

10:30 Q&A from Slides

10:40 msp432-record-demo-2

- Describe program

- Describe operation

- 8 KHz ISR tied to Timer_A1

		Listening:
			- Convert Sample Stream from Microphone
			- Explain Calibration in scaleSample
			- Records 16000 samples of 1 byte
			
		Playback
			- Use a 64 KHz PWM ON Timer_A0
			- Set duty cycle to value of sample
			
- Explain program using Timer_A Configuration

10:55 Timer_A Q&A from Slides -> Do monday