CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
93
11. Phase-Locked Loop (PLL)
This chapter presents the Phase-Locked Loop (PLL) and its associated registers. For a complete table of the PLL registers,
“Summary Table of the Core Registers” on page 36
. For a quick reference of all PSoC
®
registers in address order,
refer to the
Register Details chapter on page 125
.
11.1
Architectural Description
A
function generates the sys-
tem clock with crystal accuracy. It is designed to provide a
23.986 MHz oscillator, when utilized with an external 32.768
kHz crystal.
Although the PLL tracks crystal accuracy, it requires time to
lock onto the reference frequency when first starting. The
length of time depends on the PLLGAIN controlled by bit 7
of the OSC_CR2 register. If this bit is held low, the lock time
is less than 10 ms. If this bit is held high, the lock time is on
the order of 50 ms. After lock is achieved, it is recommended
that this bit be forced high to decrease the
on the out-
put. If longer lock time is tolerable, the PLLGAIN bit can be
held high all the time.
After the 32.768 kHz External Crystal Oscillator (ECO) has
been selected and enabled, the following procedure should
be followed to enable the PLL and allow for proper fre-
quency lock.
■
Select a CPU frequency of 3 MHz or less.
■
Enable the PLL.
■
Wait between 10 and 50 ms, depending on bit 7 of the
OSC_CR2 register.
■
Set the CPU to a faster frequency, if desired. To do this,
write the CPU Speed[2:0] bits in the OSC_CR0 register.
The CPU frequency will immediately change when these
bits are set.
Note
If the proper settings are selected in
, these steps are automatically done in
boot.asm
.
11.2
Register Definitions
The following registers are associated with the Phase Locked Loop (PLL) and are listed in address order. Each register
description has an associated register table showing the bit structure for that register. The bits that are grayed out in the
tables below are reserved bits and are not detailed in the register descriptions. Note that reserved bits should always be writ-
ten with a value of ‘0’. For a complete table of the PLL registers, refer to the
Содержание CY8C28 series
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