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ADS1258 auto-scan vs Fixed Channel

Phil B
Intellectual 540 points
Other Parts Discussed in Thread: ADS1258

Hello,

I've seen a  few questions regarding the ADS1258 operating modes but none totally answer my questions. I am trying to understand auto-scan vs fixed channel.

1. Auto-Scan mode. Meant to be used in Channel Data Read Command mode using  MUL=1, and commands

MUXDIFF, MUXSG0, MUXSG1 for set up as single ended or differential.

2. Fixed Channel mode. Meant to be used in Channel Data Read Direct mode using MUL=0 and command MUXSCH for differential channel set up.

My assumption is that Fixed Channel mode doesnt work with Channel Data Read Command mode and that conversely Auto-Scan mode doesnt work with Channel Read Direct mode. If I am wrong, I dont see how to set either of those cases up?

Thanks,

-Phil B

 

  • 0
    Intellectual 540 points

    ok, as a follow on I do see Table 17 in the spec sheet an indication that Fixed Channel should be able to work with Channel Data Read Command mode.

    So my question is what are the contents of A0-A3 in Channel Data Read Command(register format)? Are they don't cares? (Since previous command has already indicated which channel is being converted)

    Thanks,

    Phil B

  • 0 in reply to Phil B
    TI__Mastermind 44640 points

    Hi Phil,

    Channel Read Direct and Channel Read by Command modes are two different way of clocking out data. Either mode can be used in Auto-Scan or Fixed-Channel Modes.

    Read Direct requires that DIN is held constant (either HIGH or LOW). Then data is clocked out with SCLK as shown in figure 57.

    Read Direct does not require that you send a command prior to reading data. However, you could argue that technically this is a command; (even Table 14 lists these cases as commands).

    Read by Command requires that you send the read by command byte before ADC data is clocked out, as shown in figure 58. The benefit of reading data in this mode, is that you don't run the risk of getting corrupted data if your serial interface is too slow to clock out all of the data before the next conversion completes.

    The answer to your question...

    Phil B said:
    So my question is what are the contents of A0-A3 in Channel Data Read Command(register format)? Are they don't cares? (Since previous command has already indicated which channel is being converted)

    Correct! This is discussed on page 31 in the "Channel Data Read Command" section.

    The other difference to notice is in table 17 that you pointed out...depending on the MUX mode (Auto-Scan or Fixed-Channel) and the Read mode (Read Direct or Read by Command), the STATUS byte will be handled differently in each case.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Intellectual 540 points

    Chris,

    Great explanation! Thanks!

    -Phil B