24/7 Data Acquisition Wildcard Users Guide

The timeout period allowed is always great enough to account for the filter settling time (pipeline delay) after a channel is changed. The CalibrationDelay used is computed from the most recent calibration that was done, whether it pertained to the current channel or not.

Init_AD24, Use_Onboard_Ref or Use_External_Ref, and Start_Conversion or Start_Conv_With_Values must be called prior to this routine to initialize, configure, and calibrate the 24/7 Data Acquisition Wildcard.

This routine disables interrupts, then checks the data ready line (/DRDY) to see if a sample is ready. If the sample is ready, gets the sample and restores interrupts. If the data is not ready, re-enables interrupts, then calls Pause before checking the data ready line again. If the sample is not ready before the timeout value, the routine returns a 32 bit value with TIMEOUT_ERROR in the least significant byte to indicate a timeout has occurred. If the data is ready, this routine returns the conversion with 0 stored in the least significant byte. For both 16- and 24-bit resolution results the data is returned in the following 32-bit format:

WWWWWWWW XXXXXXXX YYYYYYYY ZZZZZZZZ

For a16 bit sample, WWWWWWWW is the most significant byte, XXXXXXXX is the least significant byte, YYYYYYYY is 0, and ZZZZZZZZ is the timeout flag. For a 24 bit sample, WWWWWWWW is the most significant byte, XXXXXXXX is the next significant byte, YYYYYYYY is the least significant byte, and ZZZZZZZZ is the timeout flag.

Do not call this routine from within an interrupt service routine. See Example 3 for an example of periodic use.

This routine is not re-entrant. If using in a multitasking system, be sure only one task calls this routine or be sure that separate tasks do not use the AD7714 at the same time.

AD24_Sample takes 1.18 ms to read the data ready line and will obtain a sample within 1.38 ms. The variation between the two times is due to the 200 μs time when the data ready line is high when the AD7714 is updating its output register. The full execution time of this routine if the data is ready is 1.64 ms. If data is not ready, the maximum execution time is slightly greater than the timeout period. Interrupts are disabled for a maximum of less than 400 microseconds.

FORTH: AD24_Sample_NP ( -- ud | ud = conversion result including error flag)
C: ulong AD24_Sample_NP ( void )

Identical to AD24_Sample except does not disable interrupts and does not call Pause. Do not use this routine in an interrupt service. See Example 3 for an example of periodic use.

This routine is not re-entrant. If using in a multitasking system, be sure only one task calls this routine or be sure that separate tasks do not use the AD7714 at the same time.

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