ADS8201: Using mode 5 auto trigger and auto channel and single scan mode

Hello,

There is not a lot of information in this device, but reviewing the datasheet, I believe both are needed to initiate a scan, depending on the FIFO. An SPI command is needed to intial a scan, while the CONVST pin is also needed when the FIFO is being used. 

Would you please add a SPI command, and confirm it then initiates a scan?

Regards

Cynthia

Looking further into this, I also need to point out that after the device is powered up or reset, that only registers 04h, 09h, and 09h are accessible. To write to any other register, the device must be in ADC idle mode. Note figure 27 of the datasheet. once the registers are configured, the device will then require to be put into mode 5

Based on what you said about registers being accessible only in certain states, we made the following changes to the initialization.

1. Send A000 to write 0 to reg 8 to go into IDLE mode

2. Send 8000 to write chan 0/1 config with 0

3. Send 8400 to write chan 2/3 config with 0

4. Send 8800 to write chan 4/5 config with 0

5. Send 8C00 to write chan 6/7 config with 0

6. send 9000 to set chan 0 as start channel

7. send 9406 to set reg 5 to busy active low, FIFO enabled, and use CONVST

8. send A005 to write reg 8 for mode 5.

After this setup we generate a CONVST at 1Hz, then delay 100 uS, then do 8 ADC reads.

The problems are that:

1. we always read the same value 8 times but the data should be different for the different channels.  The value seems to correspond to the first analog channel.

2. We never see Busy toggle.

We have verified that the writes to registers 5 and 8 do work since we successfully read them back after writing.  So the remaining questions are:

1. Why would Busy not toggle?  Is it not triggering even though we are using the CONVST pin pulsing low for 133ns at 1Hz rate.

2. Can CONVST be used to initiate the conversions in mode 5 or is it only a SPI command?

Any chance you can provide a valid sequence that will allow mode 5 to work and converting all 8 analog channels?

The datasheet seems to contradict itself in a number of places.

On page 17 it says that for Auto-trigger and auto channel select mode and fifo enabled, if single-scan event (mode 5) is enabled the device waits for a CONVST pulse before starting the next conversion.

On age 13 it says In Auto-Trigger with Auto-Channel Update and Single-Scan mode (Mode 5), the internal device logic triggers
conversions and all selected channels are converted sequentially. After the completion of the selected channel
conversions, an SPI command must be issued to initiate the next scan event.  It doesn't say what this "SPI command" is.

On page 14 Figure 26 shows for single scan mode that No conversions until next SCR0 write.  I assume SCR0 is referring to bit 0 of the ADC SCR register (register 5).  However it is not allowed to write to that register unless the ADC is in the IDLE state.  So on this page it talks about writing to SCR to start a convert sequence but on page15 it says conversions can be initiated by doing an ADC read command.  But if ADC read commands initiate a conversion in mode 5 then how do we read out the 8 results without initiating a new conversion sequence on each read?

Do you see where the confusion comes in?  A clean explanation of how to use mode 5 would be greatly appreciated.  Ideally using the CONVST pin to initiate conversions would work since we are using three of these devices on the board and using the common CONVST signal is nice.  But that doesn't seem to work so how should mode 5 work?

Thanks