CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
395
Analog Interface
The settings for the digital block selection are located in reg-
ister
and the 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 or more columns. However, there is a special feature
of the column clock interface logic that provides a resyn-
chronization of clock phase. This function is activated on
any I/O 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 syn-
chronous 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 pro-
cessing, as column clocks are all re-initialized and thus a
discontinuity in PHI1/PHI2 clocking will occur.
Figure 18-3. Column Clock Resynchronize on an I/O 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 that is used to perform
digital processing on the analog block outputs. Note that the
decimator function is not in the CY8C28x03 devices.
The decimator interface provides the following signals,
which are routed between the analog array and analog clock
generation circuitry to the decimator block.
1. CD: Comparator
Data
2. CLK2X: Selected analog column’s 2x clock
3. CLK:
Selected analog column’s 1x clock
4. BW
The source for the decimator data input (CD) is selected
from any of the four column comparator outputs plus several
other sources. After the source column is selected, the two
clocks associated with that column (CLK2X and CLK) are
also routed to the decimator. These clocks are by-products
of the column clock generators and are specific to the timing
of the decimator. See the Decimator chapter for details.
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 is running in
conjunction 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 out-
put latch enable signal, which transfers data from the inter-
nal accumulators 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.
Note
If the Decimation Rate bits in DECx_CR are set, then
this timer is not needed. All decimator timing is handled
internal to the decimator block.
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 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
COL CLK RESET
PHI1
IOW
PHI2
SOURCE CLOCK
Setup time to next
same input clock.
Write new clock
selection.
All clocks are
restarted in phase.
CLOCK COLUMN
REGISTER
Содержание CY8C28 series
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