CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
341
Digital Blocks
■
The comparison is DR0 > DR2, instead of DR0<= DR2
or DR0<DR2. Therefore the compare out waveform is
reversed.
■
Writing to DR2 is always buffered when PWMDBL is run-
ning. Therefore you do not need to set the register such
as in the Counter function.
■
TC and Compare are not directly available; they are only
available through the dead band function.
■
KILL modes follow dead band function’s setting.
■
KILL does not affect the counter running state except in
KILL-disable mode. The whole function is disabled when
KILL is asserted in KILL-Disable mode.
The PWMDBL dead band function is identical to the Dead
Band function, with the following exceptions:
■
No need to set ref clock input from previous block. It
derives from counter function’s compare out in current
block.
■
Dead band width selections are limited. It can be 0/1/2/4/
8/16/32/64 block clock cycles. 0 means there is no dead
band protection. DR0 is not the dead band width regis-
ter.
■
Dead band function uses the digital block clock, the
same as is used by the counter.
■
The Kill signal can act as an interrupt source.
PWMDBL may be chained in 8-bit blocks up to 32 bits.
17.1.9.1
Usability Exceptions
The following are usability exceptions for the PWMDBL
function:
1. DR0 may only be read (to transfer DR0 data to DR2)
when the block is disabled.
2. CR1 is not writeable when the PWMDBL is enabled.
17.1.9.2
Block Interrupt
The PWMDBL block has two interrupt sources. They are
identical to the Dead Band function.
17.1.10
CRCPRS Function
A Cyclic Redundancy Check/Pseudo Random Sequence
(CRCPRS) function consists of a polynomial register, a
ear Feedback Shift Register (LFSR)
, and a seed register.
.) When the CRCPRS block is
disabled and a
is written into DR2, the seed
value is also loaded into DR0. When the CRCPRS is
enabled, and synchronous clock and data are applied to the
inputs, a CRC is computed on the
data input stream.
When the data input is forced to '0', then the block functions
as a pseudo random sequencer (PRS) generator with the
output data generated at the clock rate. The most significant
bit (MSb) of the CRCPRS function is the primary output.
The CRCPRS has a selection of compare modes between
DR0 and DR2. The default behavior of the compare is
DR0==DR2. When the PRS function cycles through the
seed value as one of the valid counts, the compare output is
asserted high for one clock cycle. This is regarded as the
epoch of the pseudo random sequence. The mode bits can
be used to set other compare types. Setting Mode bit 0 to '1'
causes the compare behavior to revert to DR0 <= DR2 or
DR0 < DR2, depending upon Mode bit 1. The compare
value is the auxiliary output. An interrupt is generated on
compare true.
In PRS mode (that is, data input is fixed to zero), the Multi-
shot and KILL functions are available. These modes are
identical to the Timer/Counter function with the following
exceptions:
■
The multi-shot counter will count down when DR0 is
equal to DR2 (seed), rather than when DR0 is equal to
00h in Timer/Counter. Note that the equivalence caused
by writing DR2 in function disable mode or caused by
KILL-reload will be ignored.
■
KILL-Reload will reload DR2 data (seed) to DR0 instead
of DR1 data (period in Timer/Counter).
CRCPRS mode offers an optional Pass function. By setting
the Pass Mode bit in the CR0 register (bit 1), the CRCPRS
function is overridden. In this mode, the data input is passed
transparently to the primary output and an interrupt is gener-
ated on the rising of the data input. Similarly, the CLK input
is passed transparently to the auxiliary output. This can only
be used to pass signals to the global outputs. If the output of
a pass function is needed as an input to another digital
block, it must be resynchronized through the globals and
row inputs.
CRCPRS supports shift mode. The LFSR acts as a digital
delay line if all feedbacks are tied to zero. The shift-out data
will appear on MSB bus. Note that 'Pass' mode has higher
priority than 'Shift' mode.
Table 17-7. PWMDBL Control signals in Chained Blocks
Item
Configured in
KILL
LSB Block
START
LSB Block
Multi-shot Period
MSB Block
Dead Band Width
MSB Block
KILL Mode (in FN)
MSB Block
Clock
All Chained Blocks
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