2007-2011 Microchip Technology Inc.
DS70282E-page 89
PIC24HJ12GP201/202
EQUATION 8-2:
FOSC CALCULATION
For example, suppose a 10 MHz crystal is being used,
with “XT with PLL” being the selected oscillator mode.
If PLLPRE<4:0> = 0, then N1 = 2. This yields a
VCO input of 10/2 = 5 MHz, which is within the
acceptable range of 0.8-8 MHz.
If PLLDIV<8:0> = 0x1E, then M = 32. This yields a
VCO output of 5 x 32 = 160 MHz, which is within
the 100-200 MHz ranged needed.
If PLLPOST<1:0> = 0, then N2 = 2. This provides
a Fosc of 160/2 = 80 MHz. The resultant device
operating speed is 80/2 = 40 MIPS.
EQUATION 8-3:
XT WITH PLL MODE
EXAMPLE
FIGURE 8-2:
PIC24HJ12GP201/202 PLL BLOCK DIAGRAM
TABLE 8-1:
CONFIGURATION BIT VALUES FOR CLOCK SELECTION
FOSC
FIN
M
N1
N2
----------------------
=
FCY
FOSC
2
-------------
1
2
---
10000000
32
22
-------------------------------------
40 MIPS
==
=
Oscillator Mode
Oscillator
Source
POSCMD<1:0>
FNOSC<2:0>
Note
Fast RC Oscillator with Divide-by-N (FRCDIVN)
Internal
xx
111
1, 2
Fast RC Oscillator with Divide-by-16 (FRCDIV16)
Internal
xx
110
1
Low-Power RC Oscillator (LPRC)
Internal
xx
101
1
Secondary (Timer1) Oscillator (SOSC)
Secondary
xx
100
1
Primary Oscillator (HS) with PLL (HSPLL)
Primary
10
011
—
Primary Oscillator (XT) with PLL (XTPLL)
Primary
01
011
—
Primary Oscillator (EC) with PLL (ECPLL)
Primary
00
011
1
Primary Oscillator (HS)
Primary
10
010
—
Primary Oscillator (XT)
Primary
01
010
—
Primary Oscillator (EC)
Primary
00
010
1
Fast RC Oscillator with PLL (FRCPLL)
Internal
xx
001
1
Fast RC Oscillator (FRC)
Internal
xx
000
1
Note 1:
OSC2 pin function is determined by the OSCIOFNC Configuration bit.
2:
This is the default oscillator mode for an unprogrammed (erased) device.
0.8-8.0 MHz
Here(1)
100-200 MHz
Here(1)
Divide by
2, 4, 8
Divide by
2-513
Divide by
2-33
Source (Crystal, External Clock
PLLPRE
X
VCO
PLLDIV
PLLPOST
or Internal RC)
12.5-80 MHz
Here(1)
FOSC
Note 1:
This frequency range must be satisfied at all times.
FVCO
N1
M
N2