PIC24FJ256DA210 Datasheet, PDF (151/408 Pages) Microchip Technology – 64/100-Pin, 16-Bit Flash Microcontrollers with Graphics Controller and USB On-The-Go (OTG)

PIC24FJ256DA210 FAMILY
8.5.2 USB CLOCK GENERATION
In the USB-On-The-Go module in PIC24FJ256DA210
family of devices, the primary oscillator with the PLL
block can be used as a valid clock source for USB oper-
ation. The FRC oscillator (implemented with ±0.25%
accuracy) can be combined with a PLL block, providing
another option for a valid USB clock source. There is
no provision to provide a separate external 48 MHz
clock to the USB module. The USB module sources its
clock signal from 96 MHz PLL. Due to the requirement
that a 4 MHz input must be provided to generate the
96 MHz signal, the oscillator operation is limited to a
range of possible values. Table 8-3 shows the valid
oscillator configurations (i.e., ECPLL, HSPLL, XTPLL
and FRCPLL) for USB operation. This sets the correct
PLLDIV configuration for the specified oscillator
frequency and the output frequency of the USB clock
branch is always 48 MHz.
TABLE 8-3: VALID OSCILLATOR CONFIGURATIONS FOR USB OPERATIONS
Input Oscillator Frequency
Clock Mode
PLL Division
(PLLDIV<2:0>)
48 MHz
32 MHz
24 MHz
20 MHz
16 MHz
12 MHz
8 MHz
4 MHz
ECPLL
HSPLL, ECPLL
HSPLL, ECPLL
HSPLL, ECPLL
HSPLL, ECPLL
HSPLL, ECPLL
ECPLL, HSPLL, XTPLL, FRCPLL
ECPLL, HSPLL, XTPLL, FRCPLL
12 (111)
8 (110)
6 (101)
5 (100)
4 (011)
3 (010)
2 (001)
1 (000)
Note:
For USB devices, the use of a primary oscillator or external clock source, with a frequency above 32 MHz,
does not imply that the device’s system clock can be run at the same speed when the USB module is not
used. The maximum system clock for all PIC24F devices is 32 MHz.
8.5.3
CONSIDERATIONS FOR USB
OPERATION
When using the USB On-The-Go module in
PIC24FJ256DA210 family devices, users must always
observe these rules in configuring the system clock:
• For USB operation, the selected clock source
(EC, HS or XT) must meet the USB clock
tolerance requirements.
• The Primary Oscillator/PLL modes are the only
oscillator configurations that permit USB opera-
tion. There is no provision to provide a separate
external clock source to the USB module.
• While the FRCPLL Oscillator mode is used for
USB applications, users must always ensure that
the FRC source is configured to provide a
frequency of 4 MHz or 8 MHz (RCDIV<2:0> = 001
or 000) and that the USB PLL prescaler is
configured appropriately.
All other oscillator modes are available; however, USB
operation is not possible when these modes are
selected. They may still be useful in cases where other
power levels of operation are desirable and the USB
module is not needed (e.g., the application is sleeping
and waiting for a bus attachment).
8.5.4 GRAPHICS CLOCK GENERATION
Two stable clock signals are generated for the graphics
controller in the PIC24FJ256DA210 family of devices.
The first clock is for the graphics controller module logic
and the second clock is for the display module interface
logic that generates the signals for the display glass.
Figure 8-2 shows this logic in the graphics clock
sub-block. Both clock signals are generated either from
the Graphics Clock Option 1 (96 MHz branch) or the
Graphics Clock Option 2 (48 MHz branch). Selection is
set in the multiplexer using the G1CLKSEL
(CLKDIV<4>) control bit. Graphics controller module
logic directly uses the output of that multiplexer while
the display module interface clock is further condi-
tioned through a postscaler to generate 128 possible
frequencies. The final clock output signal is selected
through a multiplexer using the GCLKDIV<6:0>
(CLKDIV2<15:9>) control bits. The 128 selections vary
in increments of 0.25, 0.5, and 1.0. Refer to Table 8-4
for details. Note that for applications that use the
graphics controller (GFX) module, the 96 MHz PLL
must be enabled.
 2010 Microchip Technology Inc.
DS39969B-page 151