DSPIC30F5011_06 Datasheet, PDF (144/224 Pages) Microchip Technology – High-Performance, 16-bit Digital Signal Controllers

dsPIC30F5011/5013
20.2 Oscillator Configurations
20.2.1 INITIAL CLOCK SOURCE
SELECTION
While coming out of Power-on Reset or Brown-out
Reset, the device selects its clock source based on:
a) FOS<1:0> Configuration bits, which select one
of four oscillator groups, and
b) FPR<3:0> Configuration bits, which select one
of 13 oscillator choices within the primary group.
Table 20-2 shows the Configuration bit values for clock
selection.
TABLE 20-2: CONFIGURATION BIT VALUES FOR CLOCK SELECTION
Oscillator Mode
Oscillator
Source
FOS1 FOS0 FPR3 FPR2 FPR1 FPR0
OSC2
Function
EC
Primary
1
1
1
0
1
1
CLKO
ECIO
Primary
1
1
1
1
0
0
I/O
EC w/ PLL 4x
Primary
1
1
1
1
0
1
I/O
EC w/ PLL 8x
Primary
1
1
1
1
1
0
I/O
EC w/ PLL 16x
Primary
1
1
1
1
1
1
I/O
ERC
Primary
1
1
1
0
0
1
CLKO
ERCIO
Primary
1
1
1
0
0
0
I/O
XT
Primary
1
1
0
1
0
0
OSC2
XT w/ PLL 4x
Primary
1
1
0
1
0
1
OSC2
XT w/ PLL 8x
Primary
1
1
0
1
1
0
OSC2
XT w/ PLL 16x
Primary
1
1
0
1
1
1
OSC2
XTL
Primary
1
1
0
0
0
0
OSC2
FRC w/ PLL 4x
Internal FRC
1
1
0
0
0
1
I/O
FRC w/ PLL 8x
Internal FRC
1
1
1
0
1
0
I/O
FRC w/ PLL 16x
Internal FRC
1
1
0
0
1
1
I/O
HS
Primary
1
1
0
0
1
0
OSC2
LP
Secondary
0
0
—
—
—
—
(Notes 1, 2)
FRC
Internal FRC
0
1
x
x
x
x
(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: 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.
20.2.2 OSCILLATOR START-UP TIMER
(OST)
To ensure that a crystal oscillator (or ceramic resona-
tor) has started and stabilized, an Oscillator Start-up
Timer is included. It is a simple 10-bit counter that
counts 1024 TOSC cycles before releasing the oscillator
clock to the rest of the system. The time-out period is
designated as TOST. 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 oscillator, XT, XTL, and HS modes
(upon wake-up from Sleep, POR and BOR) for the
primary oscillator.
20.2.3 LP OSCILLATOR CONTROL
Enabling the LP oscillator is controlled with two elements:
1. The current oscillator group bits COSC<1:0>.
2. The LPOSCEN bit (OSCON register).
The LP oscillator is on (even during Sleep mode) if
LPOSCEN = 1. The LP oscillator is the device clock if:
• COSC<1:0> = 00 (LP selected as main oscillator)
and
• LPOSCEN = 1
Keeping the LP oscillator on at all times allows for a fast
switch to the 32 kHz system clock for lower power oper-
ation. Returning to the faster main oscillator still
requires a start-up time.
DS70116F-page 142
© 2006 Microchip Technology Inc.