I had to control an AD5061 for my latest project, so I thought I'd share a bit of code I wrote to exercise it.
I very likely could have sped this up significantly using SPI, but for this application, it didn't need to go faster than bit-banging it. The DAC itself has a maximum clocking rate of 30 MHz - well above the maximum clock rate of the ATTiny being used.
The result of this is a rail-to-rail sine wave on the DAC. The frequency of the sine wave will give you an indication of how fast the DAC write can take place. The table is 1024 entries long, so the frequency (in Hz) / 1024 is how long each DAC operation takes. On an ATMega328P running at 20 MHz, I got 44 µs.
#include <avr/io.h>
#include <avr/pgmspace.h>
#define DAC_PORT PORTB
#define DAC_CS _BV(PORTB1)
#define DAC_DO _BV(PORTB3)
#define DAC_CLK _BV(PORTB5)
const unsigned int PROGMEM sine_table[] = {
32768,32969,33170,33371,33572,33774,33975,34176,
34377,34578,34779,34980,35180,35381,35582,35782,
35982,36183,36383,36583,36782,36982,37182,37381,
37580,37779,37978,38177,38375,38573,38771,38969,
39166,39364,39561,39757,39954,40150,40346,40542,
40737,40932,41127,41321,41515,41709,41903,42096,
42288,42481,42673,42864,43056,43247,43437,43627,
43817,44006,44195,44383,44571,44759,44946,45133,
45319,45504,45690,45874,46058,46242,46425,46608,
46790,46972,47153,47333,47513,47693,47872,48050,
48228,48405,48582,48758,48933,49108,49282,49455,
49628,49800,49972,50143,50313,50483,50652,50820,
50988,51155,51321,51487,51651,51815,51979,52142,
52303,52465,52625,52785,52944,53102,53259,53416,
53572,53727,53881,54035,54188,54339,54491,54641,
54790,54939,55087,55234,55380,55525,55669,55813,
55955,56097,56238,56378,56517,56655,56793,56929,
57065,57199,57333,57466,57597,57728,57858,57987,
58115,58242,58368,58493,58618,58741,58863,58984,
59104,59224,59342,59459,59575,59691,59805,59918,
60030,60141,60251,60360,60468,60575,60681,60786,
60890,60993,61095,61195,61295,61393,61491,61587,
61682,61776,61869,61961,62052,62142,62230,62318,
62404,62490,62574,62657,62739,62820,62899,62978,
63055,63131,63206,63280,63353,63425,63495,63565,
63633,63700,63766,63830,63894,63956,64017,64077,
64136,64193,64250,64305,64359,64412,64464,64514,
64563,64611,64658,64704,64748,64791,64834,64874,
64914,64952,64990,65025,65060,65094,65126,65157,
65187,65216,65243,65269,65294,65318,65340,65362,
65382,65401,65418,65435,65450,65464,65476,65488,
65498,65507,65515,65521,65526,65530,65533,65535,
65535,65534,65532,65528,65524,65518,65511,65503,
65493,65482,65470,65457,65442,65427,65410,65391,
65372,65351,65329,65306,65282,65256,65230,65201,
65172,65142,65110,65077,65043,65008,64971,64933,
64894,64854,64813,64770,64726,64681,64635,64587,
64539,64489,64438,64386,64332,64278,64222,64165,
64107,64047,63987,63925,63862,63798,63733,63666,
63599,63530,63460,63389,63317,63244,63169,63093,
63017,62939,62860,62779,62698,62616,62532,62447,
62361,62274,62186,62097,62007,61915,61823,61729,
61635,61539,61442,61344,61245,61145,61044,60942,
60838,60734,60629,60522,60415,60306,60196,60086,
59974,59862,59748,59633,59517,59401,59283,59164,
59044,58924,58802,58679,58556,58431,58305,58179,
58051,57923,57793,57663,57532,57399,57266,57132,
56997,56861,56724,56586,56448,56308,56168,56026,
55884,55741,55597,55452,55307,55160,55013,54865,
54716,54566,54415,54264,54111,53958,53804,53650,
53494,53338,53181,53023,52864,52705,52545,52384,
52223,52060,51897,51734,51569,51404,51238,51071,
50904,50736,50568,50398,50228,50058,49886,49714,
49542,49369,49195,49020,48845,48670,48493,48317,
48139,47961,47782,47603,47424,47243,47062,46881,
46699,46517,46334,46150,45966,45782,45597,45412,
45226,45039,44852,44665,44477,44289,44101,43912,
43722,43532,43342,43151,42960,42769,42577,42385,
42192,41999,41806,41612,41418,41224,41029,40835,
40639,40444,40248,40052,39856,39659,39462,39265,
39068,38870,38672,38474,38276,38077,37879,37680,
37481,37281,37082,36882,36683,36483,36283,36083,
35882,35682,35481,35281,35080,34879,34678,34477,
34276,34075,33874,33673,33472,33271,33069,32868,
32667,32466,32264,32063,31862,31661,31460,31259,
31058,30857,30656,30455,30254,30054,29853,29653,
29452,29252,29052,28852,28653,28453,28254,28054,
27855,27656,27458,27259,27061,26863,26665,26467,
26270,26073,25876,25679,25483,25287,25091,24896,
24700,24506,24311,24117,23923,23729,23536,23343,
23150,22958,22766,22575,22384,22193,22003,21813,
21623,21434,21246,21058,20870,20683,20496,20309,
20123,19938,19753,19569,19385,19201,19018,18836,
18654,18473,18292,18111,17932,17753,17574,17396,
17218,17042,16865,16690,16515,16340,16166,15993,
15821,15649,15477,15307,15137,14967,14799,14631,
14464,14297,14131,13966,13801,13638,13475,13312,
13151,12990,12830,12671,12512,12354,12197,12041,
11885,11731,11577,11424,11271,11120,10969,10819,
10670,10522,10375,10228,10083,9938,9794,9651,
9509,9367,9227,9087,8949,8811,8674,8538,
8403,8269,8136,8003,7872,7742,7612,7484,
7356,7230,7104,6979,6856,6733,6611,6491,
6371,6252,6134,6018,5902,5787,5673,5561,
5449,5339,5229,5120,5013,4906,4801,4697,
4593,4491,4390,4290,4191,4093,3996,3900,
3806,3712,3620,3528,3438,3349,3261,3174,
3088,3003,2919,2837,2756,2675,2596,2518,
2442,2366,2291,2218,2146,2075,2005,1936,
1869,1802,1737,1673,1610,1548,1488,1428,
1370,1313,1257,1203,1149,1097,1046,996,
948,900,854,809,765,722,681,641,
602,564,527,492,458,425,393,363,
334,305,279,253,229,206,184,163,
144,125,108,93,78,65,53,42,
32,24,17,11,7,3,1,0,
0,2,5,9,14,20,28,37,
47,59,71,85,100,117,134,153,
173,195,217,241,266,292,319,348,
378,409,441,475,510,545,583,621,
661,701,744,787,831,877,924,972,
1021,1071,1123,1176,1230,1285,1342,1399,
1458,1518,1579,1641,1705,1769,1835,1902,
1970,2040,2110,2182,2255,2329,2404,2480,
2557,2636,2715,2796,2878,2961,3045,3131,
3217,3305,3393,3483,3574,3666,3759,3853,
3948,4044,4142,4240,4340,4440,4542,4645,
4749,4854,4960,5067,5175,5284,5394,5505,
5617,5730,5844,5960,6076,6193,6311,6431,
6551,6672,6794,6917,7042,7167,7293,7420,
7548,7677,7807,7938,8069,8202,8336,8470,
8606,8742,8880,9018,9157,9297,9438,9580,
9722,9866,10010,10155,10301,10448,10596,10745,
10894,11044,11196,11347,11500,11654,11808,11963,
12119,12276,12433,12591,12750,12910,13070,13232,
13393,13556,13720,13884,14048,14214,14380,14547,
14715,14883,15052,15222,15392,15563,15735,15907,
16080,16253,16427,16602,16777,16953,17130,17307,
17485,17663,17842,18022,18202,18382,18563,18745,
18927,19110,19293,19477,19661,19845,20031,20216,
20402,20589,20776,20964,21152,21340,21529,21718,
21908,22098,22288,22479,22671,22862,23054,23247,
23439,23632,23826,24020,24214,24408,24603,24798,
24993,25189,25385,25581,25778,25974,26171,26369,
26566,26764,26962,27160,27358,27557,27756,27955,
28154,28353,28553,28753,28952,29152,29352,29553,
29753,29953,30154,30355,30555,30756,30957,31158,
31359,31560,31761,31963,32164,32365,32566,32768
};
static void writeDacValue(unsigned int value) {
PORTB |= DAC_CLK;
PORTB &= ~DAC_CS;
PORTB &= ~DAC_DO;
// we're going to write a bunch of zeros. The first six are just
// padding, and the last two are power-off bits that we want to be
// always zero.
for(int i = 0; i < 8; i++) {
PORTB &= ~DAC_CLK;
PORTB |= DAC_CLK;
}
for(int i = 15; i >= 0; i--) {
if ((value >> i) & 0x1)
PORTB |= DAC_DO;
else
PORTB &= ~DAC_DO;
PORTB &= ~DAC_CLK;
PORTB |= DAC_CLK;
}
PORTB |= DAC_CS;
}
void main() {
PORTB |= DAC_CS;
DDRB = _BV(DDB1) | _BV(DDB3) | _BV(DDB5);
while(1) {
for(int i = 0; i < sizeof(sine_table) / sizeof(unsigned int); i++) {
unsigned int val = pgm_read_word(&(sine_table[i]));
writeDacValue(val);
}
}
}