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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Two Column Limited Analog System
24.1.1.4
PWM ADC Interface
The analog interface provides hardware support and signal
routing for
conversion functions,
specifically the single slope ADC. The control signals for this
interface are split between three registers: DEC_CR0,
DEC_CR1, and ACE_PWM_CR.
The analog interface has support for the single slope ADC
operation through the ability to gate the analog comparator
outputs. This gating function is required to precisely control
the digital integration period that is performed in a digital
block as part of the function. A digital block PWM or the ded-
icated ADC PWM may be used as a source to provide the
gate signal. Only one source for the gating signal can be
selected. However, the gating can be applied independently
to any of the column comparator outputs.
The CY8C28xxx devices contain a dedicated block that can
perform this PWM gating function using VC3. The VC3 sig-
nal, out of the VC3 divider block, can be further divided to
provide for gating the incremental ADC.
The ACE_PWM_CR register controls the duty cycle selec-
tion in terms of VC3 periods, as shown in the following
tables. When enabled, the PWM block becomes the source
for the incremental gating, overriding the digital block selec-
tion.
As an alternative to the PWM, the ICLKS bits, which are split
between the DEC_CR0 and DEC_CR1 registers, may be
used to select a digital block source for the incremental gat-
ing signal. Regardless of the source of the gating, the two
IGEN bits are used to independently enable the gating func-
tion on a column-by-column basis.
24.1.1.5
Analog Modulator Interface (Mod
Bits)
The Analog Modulator Interface provides a selection of sig-
nals that are routed to either of the two analog array modula-
tion control signals. There is one modulation control signal
for the CY8C28xxx Switched Capacitor block. There are
nine selections, which include the dedicated reference volt-
age generator PWM output, the analog comparator bus out-
puts (include CS comparator output), two global outputs,
and a digital block broadcast bus. The selections for all col-
umns are contained in the ACE_AMD_CR0 and
ACE_AMD_CR1 registers.
One use of the modulator interface is to provide a selectable
reference to one of the comparator inputs. This can be done
by configuring a digital block as a PWM or PRS output with
the desired duty cycle. The SC block will then give a low-
pass filtered version of this signal, which will be a DC volt-
age relative to the supply with some ripple.
24.1.1.6
Sample and Hold Feature
Sample and Hold capability can be selected for improved
analog-to-digital conversion accuracy. This is done by set-
ting the SHEN bit in the ADCx_CR register.
When enabled, this feature works in conjunction with the
selected SSADC PWM input. During the PWM high time, the
conversion is active and the sample and hold is in “hold”
mode. During the PWM low time, the conversion is inactive,
and the sample and hold circuit is in “sample” mode.
Table 24-3. PWM High Time
HI[2:0]
Description
000b
Block is not selected, input to incremental gate is from selected
digital block.
001b
High time is 1 VC3 period.
010b
High time is 2 VC3 period.
011b
High time is 4 VC3 period.
100b
High time is 8 VC3 period.
101b
High time is 16 VC3 period.
Table 24-4. PWM Low Time
LO[1:0]
Description
00b
No low time. Comparator gate is continually high.
01b
Low time is one VC3 period.
10b
Low time is two VC3 period.
11b
Low time is three VC3 period.
Summary of Contents for CY8C28 series
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