1. Home
  2. Hobby Electronics Basics
  3. A couple basic questions regarding a ADC

A couple basic questions regarding a ADC

Hi - I'm working on interfacing a TI ADS1252 ADC

formatting link
to an Atmel AVR (an 8b microcontroller, an ATMEGA48). This one was marked as having SPI, which I thought would make it easy to interface with. Now that I'm sitting down and wiring it up, I have noticed something very strange. There are only *two* digital io lines, while SPI typically has three. Can anybody tell me if the built in SPI device in an AVR will be able to handle this?

Also - it asks for a clock input, but it only has one pin for the clock. I'm used to just attaching a crystal and two capacitors for a clock signal, but that doesn't exactly seem possible with only one clock pin. So - how would I go about getting a 16Mhz clock signal?

Thanks for your help,

-Michael J. Noone

Reply to
Michael Noone
Loading thread data ...

If you are not hooking any other devices to the AVR's SPI port, it can be made to work. If the SPI bus is shared among devices, you have some work to do getting that thing to be quiet until told to speak up.

You can buy crystal oscillators at that frequency.

You're welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
Reply to
Larry Brasfield

If the pin only has one input clock pin then it is expecting a single-ended signal input and cannot be connected directly to a crystal. Some chips have two pins and allow you to connect a crystal directly (with appropriate external passives). The difference is that the feedback circuitry is inside the chip in the latter case.

A device that provides that feedback circuitry is a called an oscillator (or crystal oscillator). Its output is at some logic level (see datasheet of specific oscillator for this info). This sounds like what you need. Make sure you pick one that matches the input requirements for the chip you want to connect e.g. input voltage level, jitter, ...

James.

Reply to
James Morrison 

--
You need to supply a 16MHz clock signal to the CLK input. if you don't
already have that in your system, then you need to buy a 16MHz crystal
oscillator. Check Digi-Key, they've got bunches. Here's one:

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=182864&Row=272631&Site=US
                                      ____ 
As for the operation of SCLK and DOUT/DRDY it's all spelled out in the
data sheet at:

http://focus.ti.com/lit/ds/symlink/ads1252.pdf
                               ____  
Basically, you wait until DOUT/DRDY goes low, (which will signal the
end of a conversion, then you exercise SCLK  and data will come out of
     ____ 
dout/DRDY.
Reply to
John Fields

"Larry Brasfield" wrote in news:X%8be.21$ snipped-for-privacy@news.uswest.net:

Right now it'll be the only device on the SPI bus, so hopefully that won't be an issue.

Yes - heck I think I even have some 16Mhz crystals lying around. But my problem is that I'm used to connecting two leads from a crystal to two pins on an IC. Now there is only one pin - thus my confusion. Perhaps do you just have one pin from the crystal connected to the clock pin and also connected to a grounded capacitor, and then have the other crystal pin only connected to a grounded capacitor? Thanks,

-Michael J. Noone

Reply to
Michael Noone

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.