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Generating Sine Wave Using 8085 and DAC

Strategy

Is it possible to create a beautiful sine wave using our microprocessor or microcontroller. What strategy we want to use. According to us it is possible. To generate sine wave we have to output digital equivalent values which will represent sine wave as shown in figure. Digital data 00H represents -2.5V. The 7FH represents 0V6 and FFH represents +2.5V.

The digital equivalent for sine wave can be calculated as follows. We know that sin 0°=0 and sin 90°=1. The range in 0° to 90° is distributed over digital range of 7FH to FFH i.e.,(FFH to 7FH) 128 decimal steps. Therefore taking 128 as a offset we can write digital equivalent value for sin θ =(128+128×sin ɑ). Where ɑ  is an angle in degrees which varies from -90° to +90° with a period of 5°. By changing the value of ɑ to less than 5°, you can get more accurate sine wave. Now you have to enter DATA(approximate hex code) in corresponding memory location as shown in the table below:


Address Algle(θ) Degree(ɑ) Hex code Data
(hex code
approximate)
2500 -90 0.0 00 00
2501 -85 0.48 00 01
2502 -80 1.94 01 02
2503 -75 4.36 04 04
2504 -70 7.71 08 08
2505 -65 11.99 0B 11
2506 -60 17.14 11 17
2507 -55 23.14 17 1E
2508 -50 29.94 1D 25
2509 -45 37.49 25 2D
250A -40 45.72 2E 36
250B -35 54.58 37 40
250C -30 64.00 40 49
250D -25 73.90 4A 54
250E -20 84.22 54 5E
250F -15 94.87 5F 69
2510 -10 105.77 6A 74
2511 -05 116.84 74 7F
2512 00 128.00 80 84
2513 05 139.15 8B 95
2514 10 150.20 96 9F
2515 15 161.12 A1 AF
2516 20 171.77 A6 B4
2517 25 182.09 B6 C0
2518 30 192.00 C0 C8
2519 35 201.42 C9 D0
251A 40 210.27 D2 D8
251B 45 218.50 DA E0
251C 50 226.05 E2 EA
251D 55 232.85 E8 ED
251E 60 238.85 EE EF
251F 65 244.00 F4 F2
2520 70 248.28 F8 F9
2521 75 251.63 FB FC
2522 80 254.05 FE FD
2523 85 255.51 FF FF
2524 90 256.00 100 00
Now the program can be written as below;
Address Label Mnemonic Machine code Comments
2000 MVI A,80H 3E, 80 Initializing the ports of the PPI 8255 as O/P ports by writing the control word as 80H.
2002 0UT CWR D3, Address of CWR Control word specify the I/O function for each ports of 8255.
2004 START MVI C,24H 0E, 24
2006 LXI H,2500H 21, 00, 25
2009 POS MOV A,M 7E
200A OUT PORT A D3, address of PORT A [[H-L]] is outputted through portA
200C INX H 23
200D DCR C 0D
200E JNZ POS C2, 09, 20
2011 MVI A,24H 0E, 24
2013 NEG DCX H 2B
2014 MOV A,M 7E
2015 OUT 00H D3, Address of PORT A [[H-L]] is outputted through portA.
2017 DCR C 0D
2018 JNZ NEG C2, 13, 20
201B JMP START C3, 04, 20

Note:

  • I will suggest you to use R-2R DAC(Digital to Analog Converter) for this purpose. If you are using this R-2R DAC for this purpose it is not preferred to breadboard it. You have to solder it to avoid erroneous values.

    • R-2R ladder DAC
  • Refer your manual of microprocessor trainer kit to find out address of CWR and port A
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