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2011-2015 Microchip Technology Inc.
DS40001609E-page 49
PIC16(L)F1508/9
FIGURE 5-3:
QUARTZ CRYSTAL
OPERATION (LP, XT OR
HS MODE)
FIGURE 5-4:
CERAMIC RESONATOR
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, 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
5.4 “Two-Speed Clock Start-up Mode”
).
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.
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 Applications 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)
R
S
(1)
OSC1/CLKIN
PIC
®
MCU
OSC2/CLKOUT
Note 1:
A series resistor (Rs) 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
MΩ and
10
MΩ
).
R
F
(2)
C2
C1
To Internal
Logic
Sleep
Quartz
Crystal
Rev. 10-000059A
7/30/2013
R
S
(1)
OSC1/CLKIN
PIC
®
MCU
OSC2/CLKOUT
Note 1:
A series resistor (Rs) 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
MΩ and
10
MΩ
).
3.
An additional parallel feedback resistor (R
P
)
may be required for proper ceramic resonator
operation.
R
F
(2)
C2
C1
To Internal
Logic
Sleep
R
P
(3)
Ceramic
Resonator
Rev. 10-000060A
7/30/2013