CY8C38_1105 Datasheet, PDF (28/130 Pages) Cypress Semiconductor – Programmable System-on-Chip (PSoC) Multiply and divide instructions

PSoC^® 3: CY8C38 Family
Data Sheet
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
6.1.2.1 MHz External Crystal Oscillator
The MHzECO provides high frequency, high precision clocking
using an external crystal (see Figure 6-2). It supports a wide
variety of crystal types, in the range of 4 to 25 MHz. When used
in conjunction with the PLL, it can generate CPU and system
clocks up to the device's maximum frequency (see PLL). The
GPIO pins connecting to the external crystal and capacitors are
fixed. MHzECO accuracy depends on the crystal chosen.
Figure 6-2. MHzECO Block Diagram
4 - 25 MHz ^XCLK_MHZ
Crystal Osc
Xi
(Pin P15[1])
External
Components
Xo
(Pin P15[0])
4 –25 MHz
crystal
Capacitors
6.1.2.2 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 (see Figure 6-3). The
32kHzECO also connects directly to the sleep timer and provides
the source for the 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
neighboring circuits. The GPIO pins connected to the external
crystal and capacitors are fixed.
Figure 6-3. 32kHzECO Block Diagram
32 kHz
Crystal Osc
XCLK32K
Xi
(Pin P15[3])
External
Components
Xo
(Pin P15[2])
32 kHz
crystal
Capacitors
6.1.2.3 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 UDBs.
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.
6.1.3 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. Bus clock is the
source clock for the CPU clock divider.
„ 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 ADC 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.
Each clock divider consists of an 8-input multiplexer, a 16-bit
clock divider (divide by 2 and higher) that generates ~50 percent
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.
Document Number: 001-11729 Rev. *S
Page 28 of 130
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