Document # 001-20559 Rev. *D
15
8.
Internal Main Oscillator (IMO)
This chapter presents the Internal Main Oscillator (IMO) and its associated registers. The IMO produces clock signals of 24
MHz and 48 MHz. For a complete table of the IMO registers, refer to the
“Summary Table of the Core Registers” on page 32
For a quick reference of all PSoC registers in address order, refer to the
Register Details chapter on page 47
.
8.1
Architectural Description
The Internal Main Oscillator (IMO) outputs two clocks: a
SYSCLK, which can be the internal 24 MHz clock or an
external clock, and a SYSCLKX2 that is always twice the
SYSCLK frequency. In the absence of a high-precision input
source from the 32.768 kHz
of the internal 24/48 MHz clocks is ±2.5% over temperature
variation and two voltage ranges (3.3V ± 0.3V and 5.0V ±
0.25%). No external components are required to achieve
this level of accuracy.
There is an option to phase lock this oscillator to the Exter-
nal Crystal Oscillator (ECO). The choice of crystal and its
inherent accuracy determines the overall accuracy of the
oscillator. The ECO must be stable prior to locking the fre-
quency of the IMO to this reference source.
The frequency doubler circuit, which produces SYSCLKX2,
can be disabled to save power. The lower frequency SYS-
CLK settings are available by setting the slow IMO (SLIMO)
bit in the CPU_SCR1 register. With this bit set and the corre-
sponding factory trim value applied to the IMO_TR register,
SYSCLK can be lowered to 6 MHz. This offers lower device
power consumption for systems that can operate with the
reduced system clock. Slow IMO mode is discussed further
in the
“Application Description” on page 15
8.2
Application Description
To save power, the IMO frequency can be reduced from 24
MHz to 6 MHz or 12 MHz using the SLIMO bit in the
CPU_SCR1 register, in conjunction with the Trim values in
the IMO_TR register. Note that the CY8C27x43,
CY8C24533, CY8C23533, CY8C23433, CY8C24633,
CY8C24x23, CY8C22x13, CY7C603xx, and CYWUSB6953
devices do not have this functionality.
8.2.1
Trimming the IMO
An 8-bit register (IMO_TR) is used to trim the IMO. Bit 0 is
the LSB and bit 7 is the MSB. The trim step size is approxi-
mately 80 kHz.
A factory trim setting is loaded into the IMO_TR register at
boot time for 5V ± 0.25V operation, except for the
CY7C603xx, which is 3.3V ± 0.25V. For operation in the volt-
age ranges of 3.3V ± 0.3V and 2.7V ± 0.3V, user code must
modify the contents of this register with values stored in
Flash bank 0 as shown in
. This is
done with a Table Read command to the Supervisory ROM.
Содержание PSoC CY8C23533
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