Document # 001-20559 Rev. *D
221
Analog Interface
18.1.3
Analog Column Clock Generation
The analog array switched capacitor blocks require a two-
phase, non-overlapping clock. The switched capacitor
blocks are arranged two to a column (a third block in the col-
umn is a continuous time block).
An analog column clock generator is provided for each col-
umn and is shared among the blocks in that column. The
input clock source for each column clock generator is select-
able according to the
register. It is important to
note that regardless of the clock source selected, the output
frequency of the column clock generator is the input fre-
quency divided by four. There are four selections for each
column: V1, V2, ACLK0, and ACLK1. The V1 and V2 clock
signals are global system clocks. Programming options for
these system clocks can be accessed in the
reg-
ister. Each of the ACLK0 and ACLK1 clock selections are
driven by a selection of digital block outputs. The settings for
the digital block selection are located in register
The timing for analog column clock generation is shown in
. The dead band time between two phases of the
clock is designed to be a minimum of 21 ns.
Figure 18-2. Two Phase Non-Overlapping Clock
Generation
18.1.3.1
Column Clock Synchronization
When analog signals are routed between blocks in adjacent
columns, it is important that the clocks in these columns are
synchronized in phase and frequency. Frequency synchroni-
zation may be achieved by selecting the same input source
to two columns. However, there is a special feature of the
column clock interface logic that provides a resynchroniza-
tion of clock phase. This function is activated on any IO write
to either the Column Clock Selection register (CLK_CR0) or
the Reference Calibration Clock register (RCL_CR). A write
to either of these registers initiates a synchronous reset of
the column clock generators, restarting all clocks to a known
state. This action causes all columns with the same selected
input frequency to be in phase. Writing these registers
should be avoided during critical analog processing, as col-
umn clocks are all re-initialized and thus a discontinuity in
PHI1/PHI2 clocking occurs.
Figure 18-3. Column Clock Resynchronize on an IO Write
18.1.4
Decimator and Incremental ADC
Interface
The Decimator and Incremental ADC Interface provides
hardware support and signal routing for analog-to-digital
conversion functions, specifically the Delta Signal ADC and
the Incremental ADC. The control signals for this interface
are split between two registers: DEC_CR0 and DEC_CR1.
18.1.4.1
Decimator
The Decimator is a hardware block used to perform digital
processing on the analog block outputs.
The DCLKS0 and DCLKS1 bits, which are split between the
DEC_CR0 and DEC_CR1 registers, are used to select a
source for the decimator output latch enable. The decimator
is typically run autonomously over a given period. The
length of this period is set in a timer block that runs in con-
junction with the analog processing. At the terminal count of
this timer, the primary output goes high for one clock cycle.
This pulse is translated into the decimator output latch
enable signal, which transfers data from the internal accu-
mulators to an output buffer. The terminal count also causes
an interrupt and the CPU may read this output buffer at any
time between one latch event and the next.
18.1.4.2
Incremental ADC
The analog interface has support for the incremental ADC
operation through the ability to gate the analog comparator
outputs. This gating function is required in order to precisely
control the digital integration period that is performed in a
digital block, as part of the function. A digital block pulse
width modulator (PWM) is 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.
INPUT CLK
COL CLK
PHI1
PHI2
Underlap is
21 ns to 42 ns.
COL CLK transitions on the
falling edge of each phase.
CPUCLK
CLK24
L CLK RESET
PHI1
IOW
PHI2
URCE CLOCK
Setup time to next
same input clock.
Write new clock
selection.
All clocks are
restarted in phase.
OCK COLUMN
REGISTER
Содержание PSoC CY8C23533
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