CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
443
Two Column Limited Analog System
Figure 24-2. Single Slope ADC Block Diagram
To interface the asynchronous analog comparator to the dig-
ital block array, a double synchronization is required. As
shown in
, the PWM is also delayed to align with
the valid comparator output.
The basic conversion waveforms are shown in
The high time of the PWM is set so that the counter will
count to a full-scale value. For example, for 8-bit resolution,
the high time of the PWM corresponds to 255 (or 256) coun-
ter clocks. The low time of the PWM is designed to allow the
capacitor to discharge. When a PWM is used for continuous
conversions, the Terminal Count of the PWM can be used
as a consistent interrupt to read the result of the previous
conversion. If only a single conversion is desired, the com-
parator trip point can be used as an interrupt to signal the
end of conversion.
A trim register (ADCx_TR) is provided for each column. The
converter must be calibrated for a given maximum voltage,
resolution, and frequency of operation before use.
Figure 24-3. Basic ADC Waveforms
VIN
Counter
EN
Falling edge of selected PWM is routed to
column interrupt to signal end-of-conversion.
PWM output controls the ramp on time and discharge off time.
Synchronized PWM
is gated with analog
comparator to
enable the Counter.
To Column INT
PWM
Dedicated
ADC PWM
Start of
conversion
TC
PWM
Voltage
Ramp
Comparator
Counter Gate
Ramp voltage is equal to input
voltage and comparator trips.
End of
conversion
(max range)
Counter measures the time from the start
of the voltage ramp to the comparator trip.
Summary of Contents for CY8C28 series
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