Datasheet

© 2005 Microchip Technology Inc. DS70043F-page 19
dsPIC30F
7.0 SYSTEM INTEGRATION
System management services provided by the
dsPIC30F device family include:
• Control of clock options and oscillators
• Power-on Reset
• Programmable Brown-out Reset
• Program control of Power-up Timer
• Oscillator start-up timer/stabilizer
• Watchdog Timer with RC oscillator
• Fail-Safe Clock Monitor
• Reset by multiple sources
7.1 Clock Options and Oscillators
There are three primary clock oscillators: XTL, XT and
HS. The XTL oscillator is designed for crystals or
ceramic resonators in the range of 200 kHz to 4 MHz.
The XT oscillator is designed for crystals and ceramic
resonators in the range of 4 to 10 MHz. The HS (High-
Speed) oscillator is for crystals in the 10 to 25 MHz
range. These oscillators use the OSC1 and OSC2 pins.
The secondary (LP) oscillator is designed for low power
and uses a 32 kHz crystal or ceramic resonator. The LP
oscillator uses the SOSC1 and SOSC2 pins.
The FRC (Fast RC) internal oscillator runs at a nominal
7.37 MHz ±2%. The user software can tune the FRC
frequency. The LPRC (Low Power RC) internal
oscIllator is connected to the Watchdog Timer, and it
runs at a nominal 512 kHz. The External RC (ERC)
oscillator uses an external resistor and capacitor
connected to the OSC1 pin. Frequency of operation is
up to 4 MHz.
The OSC1 pin can also be used as an input from an
external clock source; this mode is called “EC”.
The dsPIC30F oscillator system provides:
• Various external and internal oscillator options as
clock sources
• An on-chip PLL to boost internal operating
frequency 4, 8 or 16 times
• In some devices, the FRC oscillator can also be
used with the PLL
• Clock switching between various clock sources
• Programmable clock postscaler for system power
savings
• A Fail-Safe Clock Monitor (FSCM) that detects
clock failure and takes fail-safe measures
• A Clock Control register (OSCCON)
• Nonvolatile Configuration bits for main oscillator
selection.
A simplified block diagram of the oscillator system is
shown in Figure 7-1.
7.2 Power-On Reset
When a supply voltage is applied to the device, a
Power-on Reset is generated. A new Power-on Reset
event is generated if the supply voltage falls below the
device threshold voltage (V
POR). An internal POR
pulse is generated when the rising supply voltage
crosses the POR circuit threshold voltage.
7.3 Programmable Brown-out Reset
The BOR (Brown-out Reset) module is based on an
internal voltage reference circuit. The main purpose of
the BOR module is to generate a device Reset when a
brown-out condition occurs. Brown-out conditions are
generally caused by glitches on the AC mains (i.e.,
missing portions of the AC cycle waveform due to bad
power transmission lines or voltage sags due to
excessive current draw when a large inductive load is
turned on).
The BOR module allows selection of one of the
following voltage trip points:
•2.0V
•2.7V
•4.2V
•4.5V
A BOR generates a Reset pulse, which resets the
device.
Note: The BOR voltage trip points indicated here
are nominal values provided for design
guidance only. Refer to the Electrical
Specifications in the specific device data
sheet for BOR voltage limit specifications.