 English |
|
|
|
|
|
|
|
| PIC18F2450 Datasheet, PDF (26/320 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology | |||
| |||
| ◁ |
PIC18F2450/4450
2.2.1
OSCILLATOR MODES AND
USB OPERATION
Because of the unique requirements of the USB module,
a different approach to clock operation is necessary. In
previous PICmicro® devices, all core and peripheral
clocks were driven by a single oscillator source; the usual
sources were primary, secondary or the internal
oscillator. With PIC18F2450/4450 devices, the primary
oscillator becomes part of the USB module and cannot
be associated to any other clock source. Thus, the USB
module must be clocked from the primary clock source;
however, the microcontroller core and other peripherals
can be separately clocked from the secondary or internal
oscillators as before.
Because of the timing requirements imposed by USB,
an internal clock of either 6 MHz or 48 MHz is required
while the USB module is enabled. Fortunately, the
microcontroller and other peripherals are not required
to run at this clock speed when using the primary
oscillator. There are numerous options to achieve the
USB module clock requirement and still provide
flexibility for clocking the rest of the device from the
primary oscillator source. These are detailed in
Section 2.3 âOscillator Settings for USBâ.
FIGURE 2-1:
PIC18F2450/4450 CLOCK DIAGRAM
OSC2
OSC1
Primary Oscillator
Sleep
XT, HS, EC, ECIO
T1OSO
T1OSI
Secondary Oscillator
T1OSCEN
Enable
Oscillator
PIC18F2450/4450
PLLDIV
USB Clock Source
÷ 12 111
÷ 10 110
÷ 6 101
÷ 5 100
÷4
011
÷ 3 010
USBDIV
(4 MHz Input Only)
0
96 MHz
PLL
÷2
1
÷2
001
÷ 1 000
HSPLL, ECPLL,
XTPLL, ECPIO
CPUDIV
FSEN
1
USB
Peripheral
CPUDIV
÷ 4 11
÷3
10
÷ 2 01
÷ 1 00
÷6
÷4
11
÷ 4 10
÷3
01
÷ 2 00
1
0 Primary
Clock
FOSC3:FOSC0
0
CPU
IDLEN
Peripherals
T1OSC
OSCCON<6:4>
Internal Oscillator
Internal RC Oscillator
31.25 kHz
Clock
Control
FOSC3:FOSC0 OSCCON<1:0>
Clock Source Option
for other Modules
WDT, PWRT, FSCM
and Two-Speed Start-up
DS39760A-page 24
Advance Information
© 2006 Microchip Technology Inc.
|
▷ |
German
Russian
Spanish
Italian
Polish
Chinese
Japanese
Korean
French
Portuguese