CY8C53_11 datasheet(21/106 Pages) CYPRESS

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PSoC® 5: CY8C53 Family Datasheet

Document Number: 001-66237 Rev. *A

Page 21 of 106

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.

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 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 the ADC. 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.

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.

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