Datasheet
PIC18F47J53 FAMILY
DS39964B-page 40 Preliminary 2010 Microchip Technology Inc.
3.3 Oscillator Settings for USB
When the PIC18F47J53 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 Table 3-5.
3.3.1 LOW-SPEED OPERATION
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.
See Table 3-4 and Table 3-5 for possible combinations
which can be used for low-speed USB operation.
TABLE 3-4: CLOCK FOR LOW-SPEED USB
REGISTER 3-1: OSCTUNE: OSCILLATOR TUNING REGISTER (ACCESS F9Bh)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
INTSRC PLLEN
(1)
TUN5 TUN4 TUN3 TUN2 TUN1 TUN0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 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
bit 6 PLLEN: Frequency Multiplier Enable bit
(1)
1 = 96 MHz PLL is enabled
0 = 96 MHz PLL is disabled
bit 5-0 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
Note 1: When the CFGPLLEN Configuration bit is used to enable the PLL, clearing OSCTUNE<6> will not disable
the PLL.
System Clock CPDIV<1:0> Microcontroller Clock LS48MHZ USB Clock
48 11 48 MHz 1 48/8 = 6 MHz
48 10 48/2 = 24 MHz 1 48/8 = 6 MHz
48 01 48/3 = 16 MHz 1 48/8 = 6 MHz
48 00 48/6 = 8 MHz 1 48/8 = 6 MHz
24 11 24 MHz 0 24/4 = 6 MHz
24 10 24/2 = 12 MHz 0 24/4 = 6 MHz
24 01 24/3 = 8 MHz 0 24/4 = 6 MHz
24 00 24/6 = 4 MHz 0 24/4 = 6 MHz