I want to use a DAC (MCP4725) with an Attiny84 that I am programming in the Arduino IDE. I found out that the Wire.h library doesn't work with an Attiny84, and there is a library called TinyWireS.h that is supposed to work with Attiny84. This is the link to the library on github:
I just want to write a value to the DAC, and I don't understand how to do it. There is one example program included in the TinyWireS folder, and it even says that it's not a good example! This is it:
/**
* Example sketch for writing to and reading from a slave in transactional manner
*
* On write the first byte received is considered the register addres to modify/read
* On each byte sent or read the register address is incremented (and it will loop back to 0)
*
* You can try this with the Arduino I2C REPL sketch at https://github.com/rambo/I2C/blob/master/examples/i2crepl/i2crepl.ino
* If you have bus-pirate remember that the older revisions do not like the slave streching the clock, this leads to all sorts of weird behaviour
*
* To read third value (register number 2 since counting starts at 0) send "[ 8 2 [ 9 r ]", value read should be 0xBE
* If you then send "[ 9 r r r ]" you should get 0xEF 0xDE 0xAD as response (demonstrating the register counter looping back to zero)
*
* You need to have at least 8MHz clock on the ATTiny for this to work (and in fact I have so far tested it only on ATTiny85 @8MHz using internal oscillator)
* Remember to "Burn bootloader" to make sure your chip is in correct mode
*/
/**
* Pin notes by Suovula, see also http://hlt.media.mit.edu/?p=1229
*
* DIP and SOIC have same pinout, however the SOIC chips are much cheaper, especially if you buy more than 5 at a time
* For nice breakout boards see https://github.com/rambo/attiny_boards
*
* Basically the arduino pin numbers map directly to the PORTB bit numbers.
*
// I2C
arduino pin 0 = not(OC1A) = PORTB <- _BV(0) = SOIC pin 5 (I2C SDA, PWM)
arduino pin 2 = = PORTB <- _BV(2) = SOIC pin 7 (I2C SCL, Analog 1)
// Timer1 -> PWM
arduino pin 1 = OC1A = PORTB <- _BV(1) = SOIC pin 6 (PWM)
arduino pin 3 = not(OC1B) = PORTB <- _BV(3) = SOIC pin 2 (Analog 3)
arduino pin 4 = OC1B = PORTB <- _BV(4) = SOIC pin 3 (Analog 2)
*/
#define I2C_SLAVE_ADDRESS 0x4 // the 7-bit address (remember to change this when adapting this example)
// Get this from https://github.com/rambo/TinyWire
#include <TinyWireS.h>
// The default buffer size, Can't recall the scope of defines right now
#ifndef TWI_RX_BUFFER_SIZE
#define TWI_RX_BUFFER_SIZE ( 16 )
#endif
volatile uint8_t i2c_regs[] =
{
0xDE,
0xAD,
0xBE,
0xEF,
};
volatile byte reg_position;
void requestEvent()
{
TinyWireS.send(i2c_regs[reg_position]);
// Increment the reg position on each read, and loop back to zero
reg_position = (reg_position+1) % sizeof(i2c_regs);
}
void blinkn(uint8_t blinks)
{
digitalWrite(3, HIGH);
while(blinks--)
{
digitalWrite(3, LOW);
delay(50);
digitalWrite(3, HIGH);
delay(100);
}
}
/**
* The I2C data received -handler
*
* This needs to complete before the next incoming transaction (start, data, restart/stop) does
*/
void receiveEvent(uint8_t howMany)
{
if (howMany < 1)
{
// Sanity-check
return;
}
if (howMany > TWI_RX_BUFFER_SIZE)
{
// Also insane number
return;
}
reg_position = TinyWireS.receive();
howMany--;
if (!howMany)
{
// This write was only to set the buffer for next read
return;
}
while(howMany--)
{
i2c_regs[reg_position%sizeof(i2c_regs)] = TinyWireS.receive();
reg_position++;
}
}
void setup()
{
// TODO: Tri-state this and wait for input voltage to stabilize
pinMode(3, OUTPUT); // OC1B-, Arduino pin 3, ADC
digitalWrite(3, LOW); // Note that this makes the led turn on, it's wire this way to allow for the voltage sensing above.
pinMode(1, OUTPUT); // OC1A, also The only HW-PWM -pin supported by the tiny core analogWrite
/**
* Reminder: taking care of pull-ups is the masters job
*/
TinyWireS.begin(I2C_SLAVE_ADDRESS);
TinyWireS.onReceive(receiveEvent);
TinyWireS.onRequest(requestEvent);
// Whatever other setup routines ?
digitalWrite(3, HIGH);
}
void loop()
{
/**
* This is the only way we can detect stop condition (http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=984716&sid=82e9dc7299a8243b86cf7969dd41b5b5#984716)
* it needs to be called in a very tight loop in order not to miss any.
* It will call the function registered via TinyWireS.onReceive(); if there is data in the buffer on stop.
*/
TinyWireS_stop_check();
}
Another thing is that this code is labeled as being for the Attiny85, so I'm not sure how the Attiny84 would be different.
The datasheet for the DAC I'm using is at http://ww1.microchip.com/downloads/en/DeviceDoc/22039d.pdf
Can anyone help with understanding how to use the TinyWireS library to write to a slave? Or a different method? Thank you 