CY8C32_13 Datasheet, PDF (28/121 Pages) Cypress Semiconductor – Programmable System-on-Chip (PSoC®)

PSoC^® 3: CY8C32 Family Data Sheet
6.1.1 Internal Oscillators
6.1.1.1 Internal Main Oscillator
In most designs the IMO is the only clock source required, due
to its ±2-percent accuracy. The IMO operates with no external
components and outputs a stable clock. A factory trim for each
frequency range is stored in the device. With the factory trim,
tolerance varies from ±2 percent at 3 MHz, up to ±4-percent at
24 MHz. The IMO, in conjunction with the PLL, allows generation
of other clocks up to the device's maximum frequency (see
Phase-locked Loop)
The IMO provides clock outputs at 3, 6, 12, and 24 MHz.
6.1.1.2 Clock Doubler
The clock doubler outputs a clock at twice the frequency of the
input clock. The doubler works at input frequency of 24 MHz,
providing 48 MHz for the USB. It can be configured to use a clock
from the IMO, MHzECO, or the DSI (external pin).
6.1.1.3 Phase-locked Loop
The PLL allows low-frequency, high-accuracy clocks to be
multiplied to higher frequencies. This is a tradeoff between
higher clock frequency and accuracy and, higher power
consumption and increased startup time.
The PLL block provides a mechanism for generating clock
frequencies based upon a variety of input sources. The PLL
outputs clock frequencies in the range of 24 to 50 MHz. Its input
and feedback dividers supply 4032 discrete ratios to create
almost any desired clock frequency. The accuracy of the PLL
output depends on the accuracy of the PLL input source. The
most common PLL use is to multiply the IMO clock at 3 MHz,
where it is most accurate to generate the other clocks up to the
device’s maximum frequency.
The PLL achieves phase lock within 250 µs (verified by bit
setting). It can be configured to use a clock from the IMO,
MHzECO or DSI (external pin). The PLL clock source can be
used until lock is complete and signaled with a lock bit. The lock
signal can be routed through the DSI to generate an interrupt.
Disable the PLL before entering low-power modes.
6.1.1.4 Internal Low-Speed Oscillator
The ILO provides clock frequencies for low-power consumption,
including the watchdog timer, and sleep timer. The ILO
generates up to three different clocks: 1 kHz, 33 kHz, and
100 kHz.
The 1 kHz clock (CLK1K) is typically used for a background
‘heartbeat’ timer. This clock inherently lends itself to low-power
supervisory operations such as the watchdog timer and long
sleep intervals using the central timewheel (CTW).
The central timewheel is a 1 kHz, free running, 13-bit counter
clocked by the ILO. The central timewheel is always enabled,
except in hibernate mode and when the CPU is stopped during
debug on chip mode. It can be used to generate periodic
interrupts for timing purposes or to wake the system from a
low-power mode. Firmware can reset the central timewheel.
Systems that require accurate timing should use the RTC
capability instead of the central timewheel.
The 100-kHz clock (CLK100K) can be used as a low power
master clock. It can also generate time intervals using the fast
timewheel.
The fast timewheel is a 5-bit counter, clocked by the 100-kHz
clock. It features programmable settings and automatically
resets when the terminal count is reached. An optional interrupt
can be generated each time the terminal count is reached. This
enables flexible, periodic interrupts of the CPU at a higher rate
than is allowed using the central timewheel.
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 other clocks up to the
device's maximum frequency (see “Phase-locked Loop” section
on page 28). 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.
Document Number: 001-56955 Rev. *P
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