Interface EXTERNAL ADC

[Great_Alex]

Hi to All

I need help for interface ADS7816 external ADC with 3 wire interface to ATMEL AVR ATMEGA

[Carl-NC]

Looks like the ADC has a SPI interface... does the Atmel include a SPI peripheral? If it does, that's by far the easiest way to do it. If not, you have to bit-bang.

[Great_Alex]

i test it with ATMEGA32A and the microcontroller has one SPI
to interface with SPI need 1.SCK clock 2.MOSI 3.MISO .4 SS(or Chip Select)

but the ADS7816 has only 3 pin : 1.CLOCK (get from Master) 2.(CS set by master , active low) 3. Data out
in SPI when Master send one byte to slave (ADS7816) , slave send one byte to Master (Dout) in a time
the ADS7816 has no MISO so how can i send a byte to slave and read a byte from it ?

[Mdtoday]

i test it with ATMEGA32A and the microcontroller has one SPI
to interface with SPI need 1.SCK clock 2.MOSI 3.MISO .4 SS(or Chip Select)

but the ADS7816 has only 3 pin : 1.CLOCK (get from Master) 2.(CS set by master , active low) 3. Data out
in SPI when Master send one byte to slave (ADS7816) , slave send one byte to Master (Dout) in a time
the ADS7816 has no MISO so how can i send a byte to slave and read a byte from it ?

If the Atmel is anything like most MPUs with SPI modules, if it is set as the master, it should be supplying the clock and all you need to do is activate CS line on ADC first, then do a a dummy write to SPI. The data from ADC will be clocked into Atmel SPI (MISO). so MISO on Atmel is connected to ADS7816 DO.

On Microchip (DSPIC & PIC MPUs) CS can generally be just a standard IO pin, it is probably the case with Atmel too, just check your device data sheets.

Check out this link....http://www.atmel.com/Images/doc8057.pdf

Hope this helps

Mdtoday

[Carl-NC]

I took a quick look at the 7816 data sheet and there is no need to do a write. Just take CS low and clock out the data. Very simple.

[Mdtoday]

If the AVR is the master , the dummy write to SPI initates the shift clock pulses, data is clocked into AVR, user checks SPI rec flag, then reads data register. So although nothing is connected from AVR MOSI, we still have clock. I could'nt see on the AVR data sheet where reading the SPI would supply shift clock, hence my suggestion for dummy write. Carl is right though, it is a simple proccess.

[Great_Alex]

thanks carl & mdtoday
i'll test it again and send the results .