© 2004 Microchip Technology Inc. DS70054C-page 7-9
Section 7. Oscillator
Oscillator
7
7.5 Primary Oscillator
The Primary oscillator is available on the OSC1 and OSC2 pins of the dsPIC30F device family. The
Primary oscillator has 13 Operation modes summarized in Table 7-2. In general, the Primary oscil-
lator can be configured for an external clock input, external RC network, or an external crystal.
Further details of the Primary Oscillator Operating modes are described in subsequent sections.
The FPR<3:0> configuration bits (F
OSC<3:0>) select the Operating mode of the Primary oscillator.
The dsPIC30F operates from the Primary oscillator whenever the current oscillator selection
control bits in the OSCCON register (OSCCON<13:12>) are set to ‘11b’.
Table 7-2: Primary Oscillator Operating Modes
7.5.1 Oscillator Mode Selection Guidelines
The main difference between the XT, XTL and HS modes is the gain of the internal inverter of the
oscillator circuit, which allows the different frequency ranges. In general, use the oscillator option
with the lowest possible gain that still meets specifications. This will result in lower dynamic
currents (I
DD). The frequency range of each Oscillator mode is the recommended frequency
cutoff, but the selection of a different Gain mode is acceptable as long as a thorough validation
is performed (voltage, temperature and component variations, such as resistor, capacitor and
internal oscillator circuitry).
The oscillator feedback circuit is disabled in all EC and ECIO modes. The OSC1 pin is a high
impedance input and can be driven by a CMOS driver.
The ERC and ERCIO modes provide the least expensive solution for device oscillation (only an
external resistor and capacitor is required). These modes also provide the most variation in the
oscillation frequency.
If the Primary oscillator is configured for an external clock input or an external RC network, the
OSC2 pin is not required to support the oscillator function. For these modes, the OSC2 pin can
be used as an additional device I/O pin or a clock output pin. When the OSC2 pin is used as a
clock output pin, the output frequency is F
OSC/4.
The XTL mode is a Low Power/Low Frequency mode. This mode of the oscillator consumes the
least amount of power of the three Crystal modes. The XT mode is a Medium Power/Medium
Frequency mode and HS mode provides the highest oscillator frequencies with a crystal.
The EC and XT modes that use the PLL circuit provide the highest device operating frequencies.
The oscillator circuit will consume the most current in these modes because the PLL is enabled
to multiply the frequency of the oscillator.
Oscillator
Mode
Description
OSC2 Pin
Alternate
Function
EC External clock input (0-40 MHz) F
OSC/4
ECIO External clock input (0-40 MHz), OSC2 pin is I/O I/O
EC w/ PLL 4x External clock input (4-10 MHz), OSC2 pin is I/O, 4x PLL enabled I/O
EC w/ PLL 8x External clock input (4-10 MHz), OSC2 pin is I/O, 8x PLL enabled I/O
EC w/ PLL 16x External clock input (4-7.5 MHz), OSC2 pin is I/O, 16x PLL enabled I/O
ERC External RC oscillator, OSC2 pin is F
OSC/4 output FOSC/4
ERCIO External RC oscillator, OSC2 pin is I/O I/O
XT 4 MHz-10 MHz crystal (Note 1)
XT w/ PLL 4x 4 MHz-10 MHz crystal, 4x PLL enabled (Note 1)
XT w/ PLL 8x 4 MHz-10 MHz crystal, 8x PLL enabled (Note 1)
XT w/ PLL 16x 4 MHz-7.5 MHz crystal, 16x PLL enabled (Note 1)
XTL 200 kHz-4 MHz crystal (Note 1)
HS 10 MHz-25 MHz crystal (Note 1)
Note 1: External crystal connected to OSC1 and OSC2 in these Oscillator modes.
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