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kreuzkopf
Guest
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| 10 bit DAC I2C |
 Posted: Fri Dec 05, 2003 7:36 am |
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hi everyone!
i have a pic16f73 and a tc1321 (10bit DAC)
i'm not sure how i have to send my data to the dac.
this is my test-program which doesn't work 
i hope someone can help me 
| Code: | #include <16f73.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=1000000)
#use i2c(master,SCL=PIN_C3,SDA=PIN_C4)
main()
{
while(TRUE)
{
i2c_start();
i2c_write(0x90); //address
i2c_write(0x00); //command
i2c_write(0xff); //data
i2c_write(0xff); //data
i2c_stop();
}
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Dec 05, 2003 1:27 pm |
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The delay statement below is set for 1 MHz.
I suspect that it should really be 10 MHz.
| Quote: | #include <16f73.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=1000000)
#use i2c(master,SCL=PIN_C3,SDA=PIN_C4) |
Also:
1. Do you have pullup resistors on SCL and SDA ?
You could use 4.7K resistors.
2. Do you have a Vref voltage applied to the Vref pin of the TC1321 ?
If your Vdd is +5v, then the maximum Vref voltage can be 3.8v.
You can create the Vref voltage by using two resistors to make
a voltage divider. To start, you could just grab a 2.2K and a 3.3K
resistor. This would give you a Vref of 3.0 volts. The output
voltage swing of the TC1321 would then be from 0 to 3.0 volts.
You'll notice that Microchip shows an additional amplifier following
the TC1321 in their application circuit. That's to get the output
voltage swing back up to where you'd really like it to be, since
the TC1321 itself can't do a rail-to-rail output.
3. In your code below, you're continuously writing to the DAC.
You don't really need to do that.
| Quote: | while(TRUE)
{
i2c_start();
i2c_write(0x90); //address
i2c_write(0x00); //command
i2c_write(0xff); //data
i2c_write(0xff); //data
i2c_stop();
} |
It should be sufficient to just write to it once.
main()
{
i2c_start();
i2c_write(0x90); //address
i2c_write(0x00); //command
i2c_write(0xff); //data
i2c_write(0xff); //data
i2c_stop();
while(1);
} |
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iso9001
Joined: 02 Dec 2003
Posts: 262
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| Posted: Fri Dec 05, 2003 2:12 pm |
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Personally, I dont really understand how your even working with a TC1320.... its tiny as hell... I got some samples in and hit myself in the head for not REALLY reading over the datasheet (well, they look big enough in the pic  )
If anyone is interested, Maxim makes some I2C, RailtoRail, 8/10/12 bit DACs, but in DIP sizes (8/14/16/20)...
I was wondering though, when you send command to the DAC, do you need to recieve its ACK or it that optional... Also, how long does that command last ? ie: is it momentary or does it last untill you change it or turn it off? |
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Guest
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| Posted: Mon Dec 08, 2003 3:39 am |
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i have 2k2 pullups and 3v ref voltage
i've viewed scl and sda on the oscilloscope
the signal look ok
is the code really ok? i havn't used the i2c befor  |
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