The datasheet appears to be here -
https://www.ti.com/lit/gpn/dac7571
From Page 16, the 8-bit slave address is shown as -
%100110x0
So that's either $98 or $9A, as AllyCat noted -
HI2cSetup I2CMASTER, $98, I2CSLOW, I2CBYTE
HI2cSetup I2CMASTER, $9A, I2CSLOW, I2CBYTE
Also from Page 16, data is sent as 16 bits, a two byte pair, MSB first -
%00ppdddddddddddd
Two zero bits, two control bits, 12 data bits
The control bits, Page 18, are -
%--00------------ Normal Operation
%--01------------ 1kΩ to AGND, PWD
%--10------------ 100kΩ to AGND, PWD
%--11------------ High Impedance, PWD
Normal operation would seem appropriate so the word sent can be thought of as a pure 12-bit number, 0 to 4095.
So to ramp the DAC up to full and back down again repeatedly, I would try -
Code:
#Picaxe 08M2
Symbol DEVICE_ID = $98 ; or $9A
HI2cSetup I2CMASTER, DEVICE_ID, I2CSLOW, I2CBYTE
Do
For w0 = 0 To 4095 Step 1
HI2cOut (b1,b0)
PauseUs 100
Next
For w0 = 4094 to 1 Step -1
HI2cOut (b1,b0)
PauseUs 100
Next
Loop
That will take over 4 seconds to ramp up and down, so reduce the PAUSEUS and/or increase the STEP values for faster ramping.