ADS1256: about crystal & code

Gamin Inganela

Other Parts Discussed in Thread: ADS1256, ADCPRO

Dear all,

Having received the ADS1256 units we ordered, I'm testing one out using a loadcell output (millivolt-range).

Two questions I was wondering about:

1) For the circuit layout, would it be fine to use an external 4 MHz crystal & 18pF capacitors for the XTAL pins (instead of the 7.68 MHz & 18pF capacitors recommended)?

I expect, based on reading the datasheet, that the only change apart from the sampling rate would be a doubling of the analog input impedance.

2) I have never done SPI coding to interface with an external ADC, having till now only used microcontrollers with ADCs already built-in, for data collection.

Can anyone provide Code for an example of how to set ADC register values and acquire ADC data basically? I seem to have read somewhere in the posts that TI also maintains sample code for the ADS1256...

Cheers,

Gamin

over 14 years ago

0 Tony Calabria over 14 years ago

TI__Mastermind 43915 points

Hi Gamin,

You can use a slower crystal and be fine. In fact, we specified the master clock rate as 2MHz min to 10MHz max using a external crystal so a 4MHz crystal is fine. Just note that the data rates and some of the internal timings are going to scale with the decreased crystal frequency. As for the crystal itself that you choose and the 18pF capacitors, you will need to prototype them on the board to make sure there is not a start up issue. I do not thing there will be but it is better to be safe. If you run into any problems you can try decreasing the 18pF capacitors.

As for sample code, let me try and dig around and find some MSP430 code. I attached some DSP code that we use with the TMS320C5500 DSP for our ADCPro plugin to hopefully give you some idea. If I find anything else I will post it.

Regards,

Tony Calabria

ADS1256-C5509A-CCS3v1.zip