8051 DAC Interfacing

Digital-to-Analog Converter (DAC) is a device widely used to convert digital pulses to analog signals. The number of data bit inputs decides the resolution of the DAC since the number of analog output levels is equal to 2”, where n is the number of data bit inputs. Therefore, an 8-input DAC provides 256 discrete voltage (or current) levels of output.

Let’s assume a 8-bit input DAC with reference voltage +5V and full scale output of 10V. Full-scale output of the DAC is achieved when all the data inputs of the DAC are high. The following equation is used to achieve full scale output. V_out = 5V + (5 * sin θ). To find the value sent to the DAC for various angles, we simply multiply the V_out voltage by 25.60 because there are 256 steps and full-scale V_out is 10 volts. Therefore, 256 steps /10 V = 25.6 steps per volt.

To generate sine wave, the following table is used to calculate DAC input.

Angle	Magnitude	Vout	DAC Input
0°	0	5	128
30°	0.5	7.5	192
60°	0.866	9.33	238
90°	1.0	10	255
120°	0.866	9.33	238
150°	0.5	7.5	192
180°	0	5	128
210°	-0.5	2.5	64
240°	-0.866	0.669	17
270°	-1.0	0	0
300°	-0.866	0.669	17
330°	-0.5	2.5	64
360°	0	5	128

	ORG 0H
	COUNT EQU 13
AGAIN:	MOV DPTR, #TABLE
	MOV R2, #COUNT
BACK:	CLR A
	MOVC A, @A+DPTR
	MOV P1, A
	INC DPTR
	DJNZ R2, BACK
	SJMP AGAIN

	ORG 300H
TABLE:	DB 128, 192, 238, 255, 238, 192
	DB 128, 64, 17, 0, 17, 64, 128
	END

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List of topics: 8051

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