ADC128D818 readout data format

Kikuo Mita

Other Parts Discussed in Thread: ADC128D818

The ADC128D818 is a 12 bit A/D convertor.
The datasheet insists that output of the device is mapped in 16 bit register (two 8 bits registers).
Can you let me know how 12bits data are mapped on to 16 bit register
Is the 12 bits data is mapped MSB stuffing or LSB bit stuffing, like “0000b+12 bit data” or
“12 bit data + 0000b”?

When 2.5V input is applied to the device, the readout data was 0xF9A0”.
The data seemed to be LSB stuffing.

over 12 years ago

0 Kikuo Mita over 12 years ago

TI__Intellectual 2515 points

I confirmed that the data are filled from MSB like “12 bit data + 0000b”.

Mita

0 Michael Relko over 8 years ago in reply to Kikuo Mita

Intellectual 650 points

This should have been specified in the user guide. We ran into this as well and it threw us off for awhile.

0 michael musset over 8 years ago in reply to Kikuo Mita

Expert 1135 points

Can someone confirm that :

"The ADC128D818 only updates its values approximately once per second;
reading it more often will do no harm, but will return 'old' values"

0 Michael Relko over 8 years ago in reply to michael musset

Intellectual 650 points

From the datasheet:
"A voltage conversion takes 12.2 ms, and a temperature conversion takes 3.6 ms. For example, if operating in mode 2 and three voltage channels were enabled, then each round-robin monitor would take 40.2 ms (3 x 12.2ms + 3.6ms) to complete. "

Long story short, it is slow and we eventually had to use a different part that was an order of magnitude faster.

0 Chuck Sins over 8 years ago in reply to Michael Relko

TI__Mastermind 23395 points

thanks Michael for jumping in
the device was intended to have a slow sample rate making it appropriate for sampling DC like signals in systems that can accommodate the throughput rate of the device.
Chuck

0 Michael Stout over 8 years ago in reply to michael musset

TI__Genius 16890 points

Hello,

When you use the Low Power Conversion Mode it will take about 784ms. If you are using the continuous conversion mode or the one shot mode it depends on how many channels are enabled. This is described in sections 9.2.2.2.6 and 9.2.2.2.7 in the datasheet.

It will not cause a problem reading data more than once, you just see the old data that was there.

Mike

0 michael musset over 8 years ago in reply to Michael Stout

Expert 1135 points

So, normally in the fast mode, it would take 100 ms approximately to get all values.

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ADC128D818 readout data format