ADS1298: ADS1298 Daisy Chain or Cascaded

Dear Alex,

I thank you very much for the informaiton. I can see  "To use the internal oscillator in a daisy-chain configuration, set one of the devices as the master for the clock source with the internal oscillator enabled (CLKSEL pin = 1) and the internal oscillator clock brought out of the device by
setting the CLK_EN register bit to 1. Use this master device clock as the external clock source for the other devices." Does this hold true for cascade application or just for Daisy-chain configuration alone?

Regards!!

Hi Mes,

Happy to help! Cascade means running devices in parallel and daisy chain means running devices in series, so this excerpt is describing how to use the internal clock of device 1 (master) to route to device 2(slave). This is a daisy-chain configuration using an internal clock.

Another set of examples if we're using an external clock and 2 devices:
Cascade - External clock has independent connections to device 1 and device 2.
Daisy-chain - External clock connects to device 1, device 1 connects to device 2.

Does this make sense?

Dear Alex,

I thank you very much again. Your saved lots of my time. I want to ask you one more question before I made my decision and do the hardware stuff. If I chose ADS1298 and ADS1294R and combine together serially, I read that the data will be buffered from the master device first followed by don't cares and then the data from the slave.  Each channel data seems 16 bit (4 status bit followed by 12 data bits). So how long is the don't care?? is it the same 2 byte, longer or shorter?? 

Kind regards!!

Dear Alex,

To make my previous question a little bit more clear: I am planning to combine ADS1298 and ADS1294R. Use channel I of the ADS1294R for respiration and short out the rest of the channels.

I realized that the data is like 3 bytes status | 3 bytes CH1 data | 3 bytes CH2 data | 3 bytes CH3 data | 3 bytes CH4 data | 3 bytes CH5 data | 3 bytes CH6 data | 3 bytes CH7 data | 3 bytes CH8 data for ADS1298. Then followed by (XXX) and 3 bytes status | 3 bytes CH1 data for ADS1294R as the three channels are shorted and disabled. However, how may byte is the don’t care? Is it one bit, one byte or just 3 bytes?? On page 57, it is stated that one extra SCLK is mandatory. From my understanding one SCLK is necessary to read one bit, and hence it seems the don’t care is one bit. Could you explain it a bit more??

 

Kind regards!!

Hi Mes,

Sorry for the delay in my response.

The don't care is one bit.

From the ADS1298 you will see 24bit identification + 8ch * 24bit of data = 216bits
Then you will see the one don't care bit. = 1 bit
Then you will see the data from the ADS1294R. 24bit identification + 4ch * 24bit of data = 120bits
For a total of 216+1+96 = 337bits/sample.

Even though you are shorting & disabling ch2-4 of the ADS1294R there will still be data available if you send the SCLK to collect. However, since the output will be nothing more than a string of zeros it is not necessary to collect this data and can be skipped.

Dear Alex,

Thank you very much for your detalied expression.

Does the foot print of the ADS1294R and ADS1298R different? Or the footprints can be used interchangeably?? 

Kind regards!!

Hi Mes,

Both devices have the same footprint.

When exchanging devices, keep in mind that the unused analog input pins should be connected to AVDD.

Dear Alex,

Again many thanks for the quick reply and guidance. I have one more question regarding the application of ads1294R; If I use the ads 1294R to derive the respiration signal and nothing more, could you please explain the effect of the RLD circuit. Is it possible to use the ads1294R without the reference signal of the RLD circuitry or should it be configured like its ECG counterpart? Nothing is mentioned on the manual.

Kind regards!!