SAM7S32 Atmel Corporation, SAM7S32 Datasheet - Page 188
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SAM7S32
Manufacturer Part Number
SAM7S32
Description
Manufacturer
Atmel Corporation
Specifications of SAM7S32
Flash (kbytes)
32 Kbytes
Pin Count
48
Max. Operating Frequency
55 MHz
Cpu
ARM7TDMI
Hardware Qtouch Acquisition
No
Max I/o Pins
21
Ext Interrupts
21
Usb Speed
No
Usb Interface
No
Spi
1
Twi (i2c)
1
Uart
2
Ssc
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
8
Adc Resolution (bits)
10
Adc Speed (ksps)
384
Resistive Touch Screen
No
Temp. Sensor
No
Crypto Engine
No
Sram (kbytes)
8
Self Program Memory
NO
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8/3.3
Operating Voltage (vcc)
3.0 to 3.6
Fpu
No
Mpu / Mmu
no / no
Timers
3
Output Compare Channels
3
Input Capture Channels
3
Pwm Channels
4
32khz Rtc
Yes
Calibrated Rc Oscillator
No
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24.3.2
24.3.3
24.3.4
188
SAM7S Series
Main Oscillator Startup Time
Main Oscillator Control
Main Clock Frequency Counter
Figure 24-2. Typical Crystal Connection
The startup time of the Main Oscillator is given in the DC Characteristics section of the product
datasheet. The startup time depends on the crystal frequency and decreases when the fre-
quency rises.
To minimize the power required to start up the system, the main oscillator is disabled after reset
and slow clock is selected.
The software enables or disables the main oscillator so as to reduce power consumption 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.
When enabling the main oscillator, the user must initiate the main oscillator counter with a value
corresponding to the startup time of the oscillator. This startup time depends on the crystal fre-
quency connected to the main oscillator.
When the MOSCEN bit and the OSCOUNT are written in CKGR_MOR to enable the main oscil-
lator, the MOSCS bit in PMC_SR (Status Register) is cleared and the counter starts counting
down on the slow clock divided by 8 from the OSCOUNT value. Since the OSCOUNT value is
coded with 8 bits, the maximum startup time is about 62 ms.
When the counter reaches 0, the MOSCS bit is set, indicating that the main clock is valid. Set-
ting the MOSCS bit in PMC_IMR can trigger an interrupt to the processor.
The Main Oscillator features a Main Clock frequency counter that provides the quartz frequency
connected to the Main Oscillator. Generally, this value is known by the system designer; how-
ever, it is useful for the boot program to configure the device with the correct clock speed,
independently of the application.
The Main Clock frequency counter starts incrementing at the Main Clock speed after the next ris-
ing edge of the Slow Clock as soon as the Main Oscillator is stable, i.e., as soon as the MOSCS
bit is set. Then, at the 16th falling edge of Slow Clock, the MAINRDY bit in CKGR_MCFR (Main
Clock Frequency Register) is set and the counter stops counting. Its value can be read in the
MAINF field of CKGR_MCFR and gives the number of Main Clock cycles during 16 periods of
XIN
SAM7S Microcontroller
XOUT
1K
GND
6175L–ATARM–28-Jul-11
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