ATSAM3U-EK Atmel, ATSAM3U-EK Datasheet - Page 459

• Manufacturer Part Number: ATSAM3U-EK
• Description: KIT EVAL FOR AT91SAM3U CORTEX
• Manufacturer: Atmel
• Type: MCUr

Specifications of ATSAM3U-EK

• Contents: Board
• Processor To Be Evaluated: SAM3U
• Data Bus Width: 32 bit
• Interface Type: RS-232, USB
• Operating Supply Voltage: 3 V
• Silicon Manufacturer: Atmel
• Core Architecture: ARM
• Core Sub-architecture: Cortex - M3
• Silicon Core Number: SAM3U4E
• Silicon Family Name: SAM3U
• Kit Contents: Board CD Docs
• Rohs Compliant: Yes
• For Use With/related Products: AT91SAM3U
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

27.5
27.5.1
6430D–ATARM–25-Mar-11
Divider and PLLA Block
Divider and Phase Lock Loop Programming
The PLLA embeds an input divider to increase the accuracy of the resulting clock signals. How-
ever, the user must respect the PLLA minimum input frequency when programming the divider.
Figure 27-4
Figure 27-4. Divider and PLLA Block Diagram
The divider can be set between 1 and 255 in steps of 1. When a divider field (DIV) is set to 0, the
output of the corresponding divider and the PLL output is a continuous signal at level 0. On
reset, each DIV field is set to 0, thus the corresponding PLL input clock is set to 0.
The PLLA allows multiplication of the divider’s outputs. The PLLA clock signal has a frequency
that depends on the respective source signal frequency and on the parameters DIVA and
MULA. The factor applied to the source signal frequency is (MULA + 1)/DIVA. When MULA is
written to 0, the PLLA is disabled and its power consumption is saved. Re-enabling the PLLA
can be performed by writing a value higher than 0 in the MULA field.
Whenever the PLLA is re-enabled or one of its parameters is changed, the LOCKA bit in
PMC_SR is automatically cleared. The values written in the PLLACOUNT field in CKGR_PLLAR
are loaded in the PLLA counter. The PLLA counter then decrements at the speed of the Slow
Clock until it reaches 0. At this time, the LOCK bit is set in PMC_SR and can trigger an interrupt
to the processor. The user has to load the number of Slow Clock cycles required to cover the
PLLA transient time into the PLLACOUNT field.
The PLLA clock can be divided by 2 by writing the PLLADIV2 bit in PMC_MCKR register.
shows the block diagram of the divider and PLLA block.
MAINCK
SLCK
Divider
DIVA
PLLACOUNT
Counter
PLLA
MULA
PLLA
OUTA
LOCKA
SAM3U Series
PLLACK
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