Microchip Technology AC244045 Data Sheet
PIC16(L)F1825/1829
DS41440C-page 58
2010-2012 Microchip Technology Inc.
FIGURE 5-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
OPERATION (LP, XT OR
HS MODE)
FIGURE 5-4:
CERAMIC RESONATOR
OPERATION
(XT OR HS MODE)
OPERATION
(XT OR HS MODE)
5.2.1.3
Oscillator Start-up Timer (OST)
If the oscillator module is configured for LP, XT or HS
modes, the Oscillator Start-up Timer (OST) counts
1024 oscillations from OSC1. This occurs following a
Power-on Reset (POR) and when the Power-up Timer
(PWRT) has expired (if configured), or a wake-up from
Sleep. During this time, the program counter does not
increment and program execution is suspended unless
either FSCM or Two-Speed Start-up are enabled. In
this case, the code will continue to execute at the
selected INTOSC frequency while the OST is counting.
The OST ensures that the oscillator circuit, using a
quartz crystal resonator or ceramic resonator, has
started and is providing a stable system clock to the
oscillator module.
In order to minimize latency between external oscillator
start-up and code execution, the Two-Speed Clock
Start-up mode can be selected (see
modes, the Oscillator Start-up Timer (OST) counts
1024 oscillations from OSC1. This occurs following a
Power-on Reset (POR) and when the Power-up Timer
(PWRT) has expired (if configured), or a wake-up from
Sleep. During this time, the program counter does not
increment and program execution is suspended unless
either FSCM or Two-Speed Start-up are enabled. In
this case, the code will continue to execute at the
selected INTOSC frequency while the OST is counting.
The OST ensures that the oscillator circuit, using a
quartz crystal resonator or ceramic resonator, has
started and is providing a stable system clock to the
oscillator module.
In order to minimize latency between external oscillator
start-up and code execution, the Two-Speed Clock
Start-up mode can be selected (see
).
Note 1: Quartz crystal characteristics vary
according to type, package and
manufacturer. The user should consult the
manufacturer data sheets for specifications
and recommended application.
manufacturer. The user should consult the
manufacturer data sheets for specifications
and recommended application.
2: Always verify oscillator performance over
the V
DD
and temperature range that is
expected for the application.
3: For oscillator design assistance, reference
the following Microchip Application Notes:
• AN826, “Crystal Oscillator Basics and
Crystal Selection for rfPIC
®
and PIC
®
Devices” (DS00826)
• AN849, “Basic PIC
®
Oscillator Design”
(DS00849)
• AN943, “Practical PIC
®
Oscillator
Analysis and Design” (DS00943)
• AN949, “Making Your Oscillator Work”
(DS00949)
Note 1: A series resistor (R
S
) may be required for
quartz crystals with low drive level.
2: The value of R
F
varies with the Oscillator mode
selected (typically between 2 M
to 10 M.
C1
C2
Quartz
R
S(1)
OSC1/CLKIN
R
F(2)
Sleep
To Internal
Logic
Logic
PIC
®
MCU
Crystal
OSC2/CLKOUT
Note 1: A series resistor (R
S
) may be required for
ceramic resonators with low drive level.
2: The value of R
F
varies with the Oscillator mode
selected (typically between 2 M
to 10 M.
3: An additional parallel feedback resistor (R
P
)
may be required for proper ceramic resonator
operation.
operation.
C1
C2 Ceramic
R
S(1)
OSC1/CLKIN
R
F(2)
Sleep
To Internal
Logic
Logic
PIC
®
MCU
R
P(3)
Resonator
OSC2/CLKOUT