enCoRe™ V CY7C643xx, enCoRe™ V LV CY7C604xx TRM, Document No. 001-32519 Rev *H
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8. Internal Main Oscillator (IMO)
This chapter presents the Internal Main Oscillator (IMO) and its associated registers. The IMO produces clock signals of 6,
12, and 24 MHz. For a complete table of the IMO registers, refer to the
Summary Table of the Core Registers on page 24
. For
a quick reference of all enCoRe V registers in address order, refer to the
Register Reference chapter on page 163
.
8.1
Architectural Description
The Internal Main Oscillator (IMO) outputs a clock that is
normally driven to the main system clock, SYSCLK. The
IMO clock frequency can be configured as 6, 12, or 24 MHz.
The accuracy of the internal IMO clock is approximately
±5% over temperature and voltage variation. No external
components are required to achieve this level of accuracy.
The IMO provides higher accuracies when enabled for lock-
ing to USB traffic during USB operation. See
for more information. The fre-
quency doubler circuit, which produces SYSCLKX2, can be
disabled to save power.
Registers for controlling these operations are found in the
Digital Clocks chapter on page 96
.
8.2
Application Overview
Device power may be optimized by selecting among the 24,
12, or 6 MHz settings using the SLIMO bits in the
CPU_SCR1 register in conjunction with associated trim val-
ues in the IMO_TR register. Both methods are described
later in this document.
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 60 kHz at the 24-MHz clock setting. A factory trim
setting is loaded into the IMO_TR register at boot time.
8.2.2
Engaging Slow IMO
Writing to the SLIMO bits of the CPU_SCR1 register
enables the Slow IMO feature. SLIMO settings for 6 and
12 MHz are listed in
. When changing frequency
ranges, the associated factory trim value must be loaded
into the IMO_TR register. The IMO immediately changes to
the new frequency. Factory trim settings are stored in flash
for the frequencies listed in
.
Table 8-1. IMO Frequencies
SLIMO
CY7C6xxxx
00
12
01
6
10
24
11
Reserved
