![\"P162SV\"](\"http:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/P162SV.jpg\")
<\/p>\nI bought an AD9833 DDS module from China – you know the one:<\/p>\n
<\/p>\n
I wanted to control it from an Atmel ATtiny and my weapon of choice was the ATtiny44. Now I could just have easily used an ATtiny2313 (both devices are 14-pin), but I didn’t – and I went on and built a PCB.<\/p>\n
So when I came to program the ATtiny44, I realised it does not have a proper USART-SPI-mode (which the ‘2313 does). The ATtiny44 (along with the ’24 and ’84 variants and the ATtiny85) just have the USI hardware module which can be crow-barred into service as an SPI master with some heavy lifting.<\/p>\n
Well I tried three different software libraries to try and talk to the AD9833 and failed miserably on all three counts. Getting desperate, I decided to bit-bang the AD9833 to see if it was actually working. The bit-bang worked perfectly first time and – as I do not need to write to the AD9833 at any great speed – I decided to implement the bit-bang code and forget trying to get a library to work for now – although no doubt I will need to revisit the library again at some point.<\/p>\n
This code should work on pretty much any Atmel Tiny or Mega processor.<\/p>\n
Basically, we need a processor which is running at a decent speed (8MHz in my case) and any three pins: chip-select, data and clock. We manipulate these pins in accordance with the timing\u00a0 and level requirements of the AD9833 datasheet. Level requirements are: chip-select is active low, clock is normally high and data is clocked on the falling edge of the clock. Data is clocked out MSB first.<\/p>\n
We are following the software protocol in application note AN-1070;<\/a> so to get the AD9833 to output a sinewave we need to send:<\/p>\n There is a formula on the application note to calculate the frequency Lo word and Hi word for any given frequency. I wrote a spreadsheet to work these numbers out for you. You can download the spreadsheet<\/a> or use the php calculator<\/a> wot I wrote.<\/p>\n So, let’s say we want to output a sinewave at 1000Hz. We use one of the resources above to find the register values, which are low = 0x69F1 and high = 0x4000 (assuming your module has a 25MHz crystal\/oscillator fitted!).<\/p>\n You can download the code below as a .c text file<\/a>.<\/p>\n If you are using Arduino, you can change SET(DDRA,ddsDataPin) to pinMode(ddsDataPin,OUTPUT) and SET(PORTA,ddsDataPin) to digitalWrite(ddsDataPin,HIGH), etc.<\/p>\n The ASM_NOP() function gives a single processor cycle delay (no-operation).<\/p>\n Have fun.<\/p>\n I bought an AD9833 DDS module from China – you know the one: I wanted to control it from an Atmel ATtiny and my weapon of choice was the ATtiny44. Now I could just have easily used an ATtiny2313 (both devices are 14-pin), but I didn’t – and I went on and built a PCB.\u2026 Read More »<\/a><\/span><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,5,6],"tags":[],"_links":{"self":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/853"}],"collection":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=853"}],"version-history":[{"count":23,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/853\/revisions"}],"predecessor-version":[{"id":1402,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/853\/revisions\/1402"}],"wp:attachment":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=853"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=853"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=853"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n
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<\/p>\n\n\n#define F_CPU 8000000UL\n\n#include <avr\/io>\n#include <inttypes.h>\n\n#define ddsSelectPin PA0\n#define ddsClockPin PA2\n#define ddsDataPin PA3\n\n#define ASM_NOP() asm volatile (\"nop\" :: )\n#define SET(x,y) (x|=(1<<y))\n#define CLEAR(x,y) (x&=(~(1<<y)))\n#define CHECK(x,y) (x&(1<<y))\n#define TOGGLE(x,y) (x^=(1<<y))\n\nuint16_t freqLoWord = 0x69F1; \/\/what sample frequency is this? 1kHz!\nuint16_t freqHiWord = 0x4000;\n\nvoid setDDR(void) {\n \/\/set data direction (1 = output)\n SET(DDRA, ddsSelectPin); \/\/output\n SET(DDRA, ddsDataPin); \/\/output\n SET(DDRA, ddsClockPin); \/\/output\n \/\/pullups and initial states\n SET(PORTA, ddsSelectPin); \/\/high = unselected\n SET(PORTA, ddsClockPin); \/\/high = idle\n}\n\nvoid writeSPI(uint16_t word) {\n for (uint8_t i = 0; i < 16 ; i++) {\n if(word & 0x8000) SET(PORTA,ddsDataPin); \/\/bit is 1, set high\n else CLEAR(PORTA,ddsDataPin); \/\/bit is 0, set low\n ASM_NOP();\n CLEAR(PORTA,ddsClockPin); \/\/data is valid on falling edge\n ASM_NOP();\n SET(PORTA,ddsClockPin);\n word = word<<1; \/\/shift left by 1 bit\n }\nCLEAR(PORTA,ddsDataPin); \/\/idle low\nASM_NOP();\n}\n\nvoid writeDDS() {\n CLEAR(PORTA, ddsSelectPin); \/\/low = selected\n ASM_NOP();\n writeSPI(0x2100); \/\/ enable 16bit words and set reset bit\n writeSPI(freqLoWord);\n writeSPI(freqHiWord);\n writeSPI(0xC000); \/\/ set phase register to zero\n writeSPI(0x2000); \/\/ clear reset bit => audio on\n ASM_NOP();\n SET(PORTA, ddsSelectPin); \/\/high = deselected\n}\n\nvoid setup(void) {\n setDDR();\n writeDDS();\n}\n\nint main(void) {\n setup();\n while(1);\n return 0;\n}\n\n<\/pre>\n","protected":false},"excerpt":{"rendered":"