AT91SAM7A1_05 Datasheet, PDF (59/402 Pages) ATMEL Corporation – AT91 ARM Thumb-based Microcontrollers

AT91SAM7A1
11. Clock Manager (CM)
The AT91SAM7A1 microcontroller provides:
• 32.768 kHz oscillator (real-time clock oscillator)
• 4 MHz to 16 MHz oscillator
• Programmable PLL (x2 to x20)
• Programmable master clock divider
Clock management is done through the Clock Manager (CM). This allows the user to select
between the different working modes LPM, SLM and OPE.
At power-up, the master clock oscillator and the real-time clock oscillator are enabled. As the
application may or may not use the real-time clock oscillator, the DIVCLK clock is used as the
low-frequency clock (LFCLK). This ensures that both the CORECLK and the LFCLK clock can
be used at power-up.
At power-up, the PLL is disabled (PLLSCLT = 0 in the CM_CS register) to allow the user to
select the application CORECLK frequency.
Figure 11-1. Clock Management
Oscillator
MCK
MCKI
MCKO
Master
Clock
Oscillator
(4 - 16 MHz)
Programmable
PLL
(x2 to x20)
PLLCLK
0
.2 1
0
0
1
1
0
CORECLK
CM_CS.2
1
PLLSLCT _{CM_CS.5}
PLLRC
MCKEN
PLLEN
CM_PDIV.15
PLLDIV2
DIVSLCT
CM_CS.3
LFSLCT
.N
DIVCLK
RTCKI
RTCKO
Real Time
Clock
Oscillator
(32.768 kHz)
CM_MDIV DIVEN
MDIV[6:0]
RTCK
CM_CS.6
RTCSEL
0
1
RTCSLCT
LFCLK
CM_CS.7
RTCKEN
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6048A–ATARM–03-Mar-05