Datasheet

dsPIC30F4011/4012
DS70135G-page 154 © 2010 Microchip Technology Inc.
21.2 Oscillator Configurations
21.2.1 INITIAL CLOCK SOURCE
SELECTION
While coming out of Power-on Reset or Brown-out
Reset, the device selects its clock source based on:
a) The FOS<1:0> Configuration bits that select one
of four oscillator groups.
b) The FPR<3:0> Configuration bits that select one
of 13 oscillator choices within the primary group.
The selection is as shown in Table 21-2.
21.2.2 OSCILLATOR START-UP TIMER
(OST)
In order to ensure that a crystal oscillator (or ceramic
resonator) has started and stabilized, an Oscillator
Start-up Timer (OST) is included. It is a simple, 10-bit
counter that counts 1024 T
OSC cycles before releasing
the oscillator clock to the rest of the system. The time-
out period is designated as T
OST. The TOST time is
involved every time the oscillator has to restart (i.e., on
POR, BOR and wake-up from Sleep). The Oscillator
Start-up Timer is applied to the LP, XT, XTL and HS
modes (upon wake-up from Sleep, POR and BOR) for
the primary oscillator.
TABLE 21-2: CONFIGURATION BIT VALUES FOR CLOCK SELECTION
Oscillator Mode
Oscillator
Source
FOS1 FOS0 FPR3 FPR2 FPR1 FPR0
OSC2
Function
EC Primary 1 11011 CLKO
ECIO Primary 1 11100 I/O
EC w/PLL 4x Primary
1 11101 I/O
EC w/PLL 8x Primary
1 11110 I/O
EC w/PLL 16x Primary 1 11111 I/O
ERC Primary
1 11001 CLKO
ERCIO Primary
1 11000 I/O
XT Primary 1 10100 OSC2
XT w/PLL 4x Primary
1 10101 OSC2
XT w/PLL 8x Primary
1 10110 OSC2
XT w/PLL 16x Primary 1 10111 OSC2
XTL Primary
1 10000 OSC2
HS Primary
1 10010 OSC2
FRC w/PLL 4x Primary 1 10001 I/O
FRC w/PLL 8x Primary
1 11010 I/O
FRC w/PLL 16x Primary
1 10011 I/O
LP Secondary
0 0 ————(Notes 1, 2)
FRC Internal FRC
0 1 ————(Notes 1, 2)
LPRC Internal LPRC
1 0 ————(Notes 1, 2)
Note 1: OSC2 pin function is determined by the Primary Oscillator mode selection (FPR<3:0>).
2: Note that the OSC1 pin cannot be used as an I/O pin, even if the secondary oscillator or an internal clock
source is selected at all times.