PIC18F25J50 MICROCHIP [Microchip Technology], PIC18F25J50 Datasheet - Page 40

• Manufacturer Part Number: PIC18F25J50
• Description: 28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F46J50 FAMILY
REGISTER 3-1:
3.3
When the PIC18F46J50 family devices are used for
USB connectivity, a 6 MHz or 48 MHz clock must be
provided to the USB module for operation in either
Low-Speed or Full-Speed modes, respectively. This
may require some forethought in selecting an oscillator
frequency and programming the device.
The full range of possible oscillator configurations
compatible with USB operation is shown in
3.3.1
The USB clock for Low-Speed mode is derived from the
primary oscillator or from the 96 MHz PLL. In order to
operate the USB module in Low-Speed mode, a 6 MHz
clock must be provided to the USB module. Due to the
way the clock dividers have been implemented in the
DS39931D-page 40
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
bit 6
bit 5-0
INTSRC
R/W-0
Oscillator Settings for USB
LOW-SPEED OPERATION
INTSRC: Internal Oscillator Low-Frequency Source Select bit
1 = 31.25 kHz device clock derived from 8 MHz INTOSC source (divide-by-256 enabled)
0 = 31 kHz device clock derived directly from INTRC internal oscillator
PLLEN: Frequency Multiplier Enable bit
1 = 96 MHz PLL is enabled
0 = 96 MHz PLL is disabled
TUN<5:0>: Frequency Tuning bits
011111 = Maximum frequency
011110
•
•
•
000001
000000 = Center frequency; oscillator module is running at the calibrated frequency
111111
•
•
•
100000 = Minimum frequency
PLLEN
R/W-0
OSCTUNE: OSCILLATOR TUNING REGISTER (ACCESS F9Bh)
W = Writable bit
‘1’ = Bit is set
R/W-0
TUN5
Table
R/W-0
TUN4
3-5.
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
R/W-0
TUN3
PIC18F46J50 family, the microcontroller core must run
at 24 MHz in order for the USB module to get the 6 MHz
clock needed for low-speed USB operation. Several
clocking schemes could be used to meet these two
required conditions. See
possible combinations which can be used for
low-speed USB operation.
TABLE 3-4:
Clock
Input
48
24
Clock
CPU
24
24
R/W-0
TUN2
CLOCK FOR LOW-SPEED USB
CPDIV<1:0>
 2011 Microchip Technology Inc.
x = Bit is unknown
Table 3-4
‘10’
‘11’
R/W-0
TUN1
and
48/8 = 6 MHz
24/4 = 6 MHz
USB Clock
Table 3-5
R/W-0
TUN0
bit 0
for