CY8C54 CYPRESS [Cypress Semiconductor], CY8C54 Datasheet - Page 21

• Manufacturer Part Number: CY8C54
• Description: Programmable System-on-Chip (PSoC)
• Manufacturer: CYPRESS [Cypress Semiconductor]

The central timewheel can be programmed to wake the system
periodically and optionally issue an interrupt. This enables
flexible, periodic wakeups from low power modes or coarse
timing applications. Systems that require accurate timing should
use the Real Time Clock capability instead of the central
timewheel.
The 100 kHz clock (CLK100K) works as a low power system
clock to run the CPU. It can also generate time intervals such as
fast sleep intervals using the fast timewheel.
The fast timewheel is a 100 kHz, 5-bit counter clocked by the ILO
that can also be used to wake the system. The fast timewheel
settings are programmable, and the counter automatically resets
when the terminal count is reached. This enables flexible,
periodic wakeups of the CPU at a higher rate than is allowed
using the central timewheel. The fast timewheel can generate an
optional interrupt each time the terminal count is reached.
The 33 kHz clock (CLK33K) comes from a divide-by-3 operation
on CLK100K. This output can be used as a reduced accuracy
version of the 32.768 kHz ECO clock with no need for a crystal.
6.1.2 External Oscillators
6.1.2.5 MHz External Crystal Oscillator
The MHzECO provides high frequency, high precision clocking
using an external crystal. It supports a wide variety of crystal
types, in the range of 4 to 33 MHz. When used in conjunction
with the PLL, it can synthesize a wide range of precise clock
frequencies up to 80 MHz. The GPIO pins connecting to the
external crystal and capacitors are fixed. MHzECO accuracy
depends on the crystal chosen.
6.1.2.6 Digital System Interconnect
The DSI provides routing for clocks taken from external clock
oscillators connected to I/O. The oscillators can also be
generated within the device in the digital system and Universal
Digital Blocks.
While the primary DSI clock input provides access to all clocking
resources, up to eight other DSI clocks (internally or externally
generated) may be routed directly to the eight digital clock
dividers. This is only possible if there are multiple precision clock
sources.
6.1.2.7 32.768 kHz ECO
The 32.768 kHz External Crystal Oscillator (32kHzECO)
provides precision timing with minimal power consumption using
an external 32.768 kHz watch crystal. The 32kHzECO also
connects directly to the sleep timer and provides the source for
the Real Time Clock (RTC). The RTC uses a 1 second interrupt
to implement the RTC functionality in firmware.
The oscillator works in two distinct power modes. This allows
users to trade off power consumption with noise immunity from
Document Number: 001-55036 Rev. *A
PRELIMINARY
neighboring circuits. The GPIO pins connected to the external
crystal and capacitors are fixed.
6.1.3 Clock Distribution
All seven clock sources are inputs to the central clock distribution
system. The distribution system is designed to create multiple
high precision clocks. These clocks are customized for the
design’s requirements and eliminate the common problems
found with limited resolution prescalers attached to peripherals.
The clock distribution system generates several types of clock
trees.
Each clock divider consists of an 8-input multiplexer, a 16-bit
clock divider (divide by 2 and higher) that generates ~50% duty
cycle clocks, system clock resynchronization logic, and deglitch
logic. The outputs from each digital clock tree can be routed into
the digital system interconnect and then brought back into the
clock system as an input, allowing clock chaining of up to 32 bits.
6.1.4 USB Clock Domain
The USB clock domain is unique in that it operates largely
asynchronously from the main clock network. The USB logic
contains a synchronous bus interface to the chip, while running
on an asynchronous clock to process USB data. The USB logic
requires a 48 MHz frequency. This frequency can be generated
from different sources, including DSI clock at 48 MHz or doubled
value of 24 MHz from internal oscillator, DSI signal, or crystal
oscillator.
The system clock is used to select and supply the fastest clock
in the system for general system clock requirements and clock
synchronization of the PSoC device.
Bus Clock 16-bit divider uses the system clock to generate the
system’s bus clock used for data transfers and the CPU. The
CPU clock is directly derived from the bus clock.
Eight fully programmable 16-bit clock dividers generate digital
system clocks for general use in the digital system, as
configured by the design’s requirements. Digital system clocks
can generate custom clocks derived from any of the seven
clock sources for any purpose. Examples include baud rate
generators, accurate PWM periods, and timer clocks, and
many others. If more than eight digital clock dividers are
required, the Universal Digital Blocks (UDBs) and fixed function
Timer/Counter/PWMs can also generate clocks.
Four 16-bit clock dividers generate clocks for the analog system
components that require clocking, such as ADCs and mixers.
The analog clock dividers include skew control to ensure that
critical analog events do not occur simultaneously with digital
switching events. This is done to reduce analog system noise.
PSoC
®
5: CY8C54 Family Data Sheet
Page 21 of 93
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