AD7799: Changing channels

Document created by analog-archivist Employee on Feb 23, 2016
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Works 100% in a single channel application. Am trying to switch channels on the
fly. Will allow me to change channels on initialisation but not during run
time?

 

When the channel is changed with this family of products, the ADC is
automatically reset.  So, the first conversion after a channel change will
always be valid.  The time for the first conversion after the channel change is
2/Fadc while subsequent conversions will occur at Fadc.

Assuming that you are operating the AD7799 in continuous conversion mode, and
at the same update rate for each channel, switching channel involves a write to
the AD7799 configuration register. The following sequence should be followed:

(1).Write 0x0710 to the configuration register to enable AIN1(+) - AIN1(-) in
bipolar mode, buffer enabled, at a gain of 128.

(2).Continuously read the DRDY pin on the AD7799. When this pin goes low it
means that valid data from the enabled channel is available and can be read
form the AD7799 data register.

(3).Read and record the data from the data register.

Repeat steps 2 and 3 until you want to change channel and gain.

(4).If you now want to change channel, (to channel 2) write 0x0011 to the
configuration register to enable AIN2(+) -AIN2(-), bipolar mode, buffer enabled
at a gain of 1.

Repeat steps 2 and 3 until you want to change channel and gain. (Go back to
step 1)

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