The 8051 Microcontroller and Embedded

Department of Computer Science and Information EngineeringNational Cheng Kung University

13

INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL

+5V^206789194351210

10kPOT 10k150 pF

To LEDs normallyopenSTART

Vin(+)D0D1Vin(-)D2A GNDD3/2VrefD4CLK RD5D6D7CLK inCSRDD GND

+5V power supply or a reference voltage when V/2 input is open ref(not connected)VCC^1817161514131211 WRINTR

Differential analog inputs where Vin(-)= V(+) – VininVin (-) is connected to ground and Vin(+) is used as the analog input to be convertedCS is an active low input used to activate ADC804“end of conversion”When the conversion is finished, it goes low to signal the CPU that the converted data is ready to be picked up

“output enable”a high-to-low RD pulse is used to get the 8-bit converted data out of ADC804

“start conversion”When WR makes a low-to-high transition, ADC804 starts converting the analog input value of V

to an 8-in

bit digital number

Department of Computer Science and Information EngineeringNational Cheng Kung University

14

‰INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL

CLK IN and CLK R¾CLK IN is an input pin connected to an external clock source¾To use the internal clock generator (also called self-clocking), CLK IN and CLK R pins are connected to a capacitor and a resistor, and the clock frequency is determined by ƒTypical values are R = 10K ohms and C = 150 pFƒWe get

(^1) =fRC (^1). (^1) = 606 kHz and the conversion time f μsis 110
+5V^20 VCC 618 D0Vin(+) 717 D1Vin(-)^168 D2A GND^159 D3/2V^14 refD4 1913 CLK RD5^12 D6^11 D7 43 CLK inWR^5 INTR 1 CS 2 RD 10 D GND
Department of Computer Science and Information EngineeringNational Cheng Kung University
15
‰INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL
Vref/2¾It is used for the reference voltageƒIf this pin is open (not connected), the analog input voltage is in the range of 0 to 5 volts (the same as the Vcc pin)ƒIf the analog input range needs to be 0 to 4 volts, V
ref/2 is connected to 2 volts
Vref/2 Relation to V
inRange 1/256=3.900 to 1
0.5
2/256=7.81
0 to 2
1.0
2.56/256=10
0 to 2.56
1.28
3/256=11.71
0 to 3
1.5
4/255=15.62
0 to 4
2.0
5/256=19.53
0 to 5
Not connected*
Step Size ( mV)
Vin(V)
Vref/2(v) Step size is the smallest change
can be discerned by an ADC
+5V^20 VCC 618 Vin(+)D0 717 D1Vin(-)^168 D2A GND^159 D3^14 /2VrefD4 1913 CLK RD5^12 D6^11 D7 4 CLK in^3 WR^51 INTRCS 2 RD 10 D GND
Department of Computer Science and Information EngineeringNational Cheng Kung University
16
‰INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL
D0-D7¾The digital data output pins¾These are tri-state buffered ƒThe converted data is accessed only when CS = 0 and RD is forced low¾To calculate the output voltage, use the following formulaƒDout
= digital data output (in decimal), ƒVin= analog voltage, and ƒstep size(resolution) is the smallest change
V sizestep
D
in=out
+5V^20 VCC 618 D0Vin(+) 717 D1Vin(-) 816 D2A GND^159 D3/2V^14 refD4 1913 CLK RD5^12 D6^11 D7 4 CLK in^3 WR^51 INTRCS 2 RD 10 D GND