at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 130

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Main Oscillator
Main Oscillator Connections
Main Oscillator Startup Time
Main Oscillator Control
130
AT91RM3400
Figure 38 shows the Main Oscillator block diagram.
Figure 38. Main Oscillator Block Diagram
The Clock Generator integrates a Main Oscillator that is designed for a 3 to 20 MHz fun-
damental crystal. The typical crystal connection is illustrated in Figure 39. The 1 k
resistor is only required for crystals with frequencies lower than 8 MHz. The oscillator
contains twenty-five pF capacitors on each XIN and XOUT pin. Consequently, CL1 and
CL2 can be removed when a crystal with a load capacitance of 12.5 pF is used. For fur-
ther details on the electrical characteristics of the Main Oscillator, see the section “DC
Characteristics” on page 432.
Figure 39. Typical Crystal Connection
The startup time of the Main Oscillator is given in the section “DC Characteristics” on
page 432. The startup time depends on the crystal frequency and increases when the
frequency rises.
To minimize the power required to start up the system, the Main Oscillator is disabled
after reset and the Slow Clock mode is selected.
The software enables or disables the Main Oscillator so as to reduce power consump-
tion by clearing the MOSCEN bit in the Main Oscillator Register (CKGR_MOR). When
disabling the Main Oscillator by clearing the MOSCEN bit in CKGR_MOR, the MOSCS
bit in PMC_SR is automatically cleared indicating the Main Clock is off.
XIN
XOUT
Clock
Slow
C
L1
XIN
OSCOUNT
Main Clock
MOSCEN
Frequency
Oscillator
Oscillator
Counter
Counter
Main
XOUT
Main
C
L2
1K
Clock
Main
MAINRDY
MOSCS
MAINF
GNDPLL
1790A–ATARM–11/03