atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 39

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

6.9.3
7766A–AVR–03/08
PLL Frequency Control Register – PLLFRQ
• Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started. Note that the Calibrated 8 MHz Internal RC oscillator is
automatically enabled when the PLLE bit is set and with PINMUX (see PLLFRQ register) is set.
The PLL must be disabled before entering Power down mode in order to stop Internal RC Oscil-
lator and avoid extra-consumption.
• Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock. After the PLL is enabled, it
takes about several ms for the PLL to lock. To clear PLOCK, clear PLLE.
• Bit 7– PINMUX: PLL Input Multiplexer
This bit selects the clock input of the PLL:
• Bit 6– PLLUSB: PLL Postcaler for USB Peripheral
This bit select the division factor between the PLL output frequency and the USB module input
frequency:
• Bit 5..4 – PLLTM1:0: PLL Postcaler for High Speed Timer
These bits codes for the division factor between the PLL Output Frequency and the High Speed
Timer input frequency.
Note that the division factor 1.5 will introduce some jitter in the clock, but keeping the error null
since the average duty cycle is 50%. See
Bit
$32
Read/Write
Initial Value
PLLTM1
0
0
1
1
– PINMUX = 0: the PLL input is connected to the PLL Prescaler, that has the Primary
– PINMUX = 1: the PLL input is directly connected to the Internal Calibrated 8MHz RC
– PLLUSB = 0: no division, direct connection (if PLL Output = 48 MHz)
– PLLUSB = 1: PLL Output frequency is divided by 2 and sent to USB module (if PLL
System Clock as source
Oscillator. This mode allows to work in USB Low Speed mode with no crystal or
using a crystal with a value different of 8/16MHz.
Output = 96MHz)
PLLTM0
7
PINMUX
R/W
0
0
1
0
1
6
PLLUSB
R/W
0
PLL Postcaler Factor for High-Speed Timer
5
PLLTM1
R/W
0
0 (Disconnected)
4
PLLTM0
R/W
0
Figure 6-5
1.5
1
2
3
R/W
0
PDIV3
for more details.
2
R/W
1
PDIV2
1
R/W
0
PDIV1
ATmega32U4
0
R/W
0
PDIV0
PLLFRQ
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