In this circuit, an HA-4900 series comparator is used in conjunction with a D/A converter to form a simple,
versatile, multichannel analog input for a data acquisition system. The
processor first sends an address to the D/A, then the processor reads
the digital word generated by the comparator outputs, lb perform a
simple comparison, the processor sets the D/A to a given reference
level, then examines one or more comparator outputs to determine if the
inputs are above or below the reference. A window comparison consists of
two such cycles with two reference levels set by the D/A. One way to
digitize the inputs would be for the processor to increment the D/A in
steps. The D/A address, as each comparator switches, is the digitized
level of the input. While stairstepping, the D/A is slower than
successive approximation; all channels are digitized during one
staircase ramp.
