1. ADC and DAC Data Converter
Explain the introduction to ADC, ADC characteristics, Programming ADC using PIC18, Introduction to DAC and DAC interfacing with PIC18.
ADC and DAC Data Converter

2. Objectives Discuss the ADC of the PIC18
Explain the process of data acquisition using ADC
Program the PIC18’s ADC in assembly
Describe the basic operation of DAC
Interface a DAC chip to the PIC18

3. Introduction to ADC Digital Computer: Binary (discrete) values
Physical World: Analog (continuous) values
Example: Temperature, Humidity, Pressure
Output: Voltage or Current
Microcontroller? -----> Digital
Therefore, ADC is needed to translate (convert) the analog signals to digital numbers

4. Introduction to ADC (Cont’d)
Microcontroller Connection to Sensor via ADC

5. ADC Resolution n-bit No. of steps Step size (mV) 8 28 = 256
5/256 = 19.53 10
210 = 1024
5/1024 = 4.88 12
212 = 4096
5/4096 = 1.2
Assuming VREF = 5V
* Step Size (Resolution): is the smallest change that can be discerned by an ADC

6. ADC Reference Voltage (Vref)
Vref: Input voltage used for the reference voltage
The voltage connected to this pin , with the resolution of the ADC chip, dictate the step size
Example: If we need the analog input to be 0 to 4 volts, Vref is connected to 4 volts
Digital data output: 8-bit (D0-D7), 10-bit (D0-D9)

7. ADC Reference Voltage (Vref) (Cont’d)
Vref (V)
Vin (V)
Step size (mV)
5.00
0 to 5
5/1024 = 4.88
4.096
0 to 4.096
4.096/1024 = 4
3.0
0 to 3
3/1024 = 2.93
2.56
0 to 2.56
2.56/1024 = 2.5
2.048
0 to 2.048
2.048/1024 = 2
Vref Relation to Vin Range for an 10-bit ADC

8. ADC Digital Data Output
Dout = Vin / Step Size
Analog Input Voltage
Digital data output (in decimal):
8-bit (D0-D7)= 256
10-bit (D0-D9) = 1024
Example:
Vref = 2.56, Vin = 1.7V.
Calculate the Do-D9 output?
Solution:
Step Size = 2.56/1024 = 2.5mV
Dout = 1.7/2.5mV = 680 (Decimal)
D0-D9 =

9. Parallel versus Serial ADC

10. PIC18F4580 ADC Features

11. PIC18F4580 ADC Features (cont’d)
It has 11 analog input channels (AN0 – AN10)
10-bit ADC
Converted values are stored in ADRESH:ADRESL registers

12. ADC: Important Registers
A/D Control Register 0 (ADCON0)
Controls the operation of the A/D module
A/D Control Register 1 (ADCON1)
Configures the functions of the port pins
A/D Control Register 2 (ADCON2)
Configures the A/D clock source, programmed acquisition time and justification

13. A/D Control Register 0 (ADCON0)
Example:
ADCON0 =
Different from the Book!

14. A/D Control Register 1 (ADCON1)
* Different from the Book!

15. ADC PCFGs
Example:
ADCON1 =
* Different from the Book!

16. A/D Control Register 2 (ADCON2)
Example:
ADCON2 =
* Different from the Book!

17. ADFM Bit and ADRESx Registers
ADC ADFM Bit
ADFM Bit and ADRESx Registers

18. Example 1
For a PIC18-based system, we have Vref = Vdd = 5V. Find a) The step size and b) The ADCON1 value if we need 3 channels.
The step size = 5/1024 = 4,8mV
ADCON1 =

19. ADC Conversion Time Define in term of Tad (Conversion time per bit)
To calculate: FOSC/2, FOSC/4, FOSC/8, FOSC/16, FOSC/32 or FOSC/64

20. Steps in Programming the ADC using Pooling
TURN ON the ADC module (BSF ADCON0, ADON)
Make the ADC channel pin as input pin
Select voltage reference and ADC channel
Select the conversion speed
Wait for the required acquisition time
Activate the start conversion bit of GO/DONE
Wait for the conversion to be completed by pooling the end-of-conversion GO/DONE bit
After the GO/DONE bit has gone LOW, read the ADRESL and ADRESH register

21. Example 2 OV ER CALL DELAY ORG 0000H BSF ADCON0, GO CLRF TRISC
BACK BTFS ADCON0, GONE
BRA BACK
MOVFF ADRESL, PORTC
MOVFF ADRESH, PORTD
CALL QSEC_DELAY
BRA OVER
END
ORG 0000H
CLRF TRISC
CLRF TRISD
BSF TRISA, 0
MOVLW 0x00
MOVWF ADCON0
MOVLW 0x0E
MOVWF ADCON1
MOVLW 0xBE
MOVWF ADCON2

22. Programming ADC using Interrupts
Flag Bit
Register
Enable Bit
ADIF (ADC)
ADIF
PIR1
ADIE
PIE1
ADC Interrupt Flag Bits and Associated Registers
* Please see Program 13-2 page 514

23. Introduction to DAC Covert digital pulses to analog pulses
DAC0808 chip: Use R/2R method, 8-bit
DAC Block Diagram

24. DAC Application

25. Iref = Generally set to 2.0mA
DAC 0808
The digital inputs are converted to current (Iout)
Connecting a resistor to the Iout pin, we convert the result to voltage
This will course inaccuracy because the Resistance will affect the reading
Iout = Iref (D7/2 + D6/4 + D5/8 + D4/16 + D3/32 + D2/64 + D1/128 + D0/256)
Iref = Generally set to 2.0mA

26. PIC18 Connection to DAC0808 and Op-Amp
Example:
Binary input:
Iout = 2mA (153/256) = 1.195mA
and
Vout = 1.195mA x 5K = 5.975V

27. ADC Sensor Interfacing
Gas Sensor
Sonar Sensor
Humidity Sensor
Temperature Sensor

28. ADC Sensor Interfacing (Cont’d)
Characteristic:
Precision integrated-circuit
Output voltage is linearly proportional to the Celcius
Requires no external calibration (Internally calibration)
Output: 10mV for each degree

29. ADC Sensor Interfacing (Cont’d)
10mV = 1 degree (Minimum)
20mV = 2 degree
30mV = 3 degree .
1000mV = 100 degree (Maximum)
How to set Vref?? 5V
Step Size = 4.8mV
Vin (max) = 5V
Which one suitable?
Vref = ???
1.024
Step Size = 1mV
Vin (max) = 1.024V

30. ADC Sensor Interfacing (Cont’d)
To overcome any fluctuations in power supply.
* Please see Program 13-4 page 524

31. “Things are only impossible until they're not”
End of Chapter