PIC16C745/765
13.2
Oscillator Configurations
TABLE 13-1: CERAMIC RESONATORS
Ranges Tested:
13.2.1
OSCILLATOR TYPES
Mode
Freq
OSC1
OSC2
The PIC16C745/765 can be operated in four different
oscillator modes. The user can program a configuration
bit (FOSC0) to select one of these four modes:
HS
6.0 MHz
TBD
TBD
These values are for design guidance only. See notes at
bottom of page.
•EC
•E4
•HS
•H4
External Clock
TABLE 13-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
External Clock with PLL
High Speed Crystal/Resonator
High Speed Crystal/Resonator with PLL
Osc Type
Crystal
Freq
Cap. Range
C1
Cap. Range
C2
13.2.2 CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
TBD
TBD
HS
6.0 MHz
These values are for design guidance only. See notes at
bottom of page.
In HS mode, a crystal or ceramic resonator is con-
nected to the OSC1/CLKIN and OSC2/CLKOUT pins to
establish oscillation (Figure 13-1). The PIC16C745/
765 oscillator design requires the use of a parallel cut
crystal. Use of a series cut crystal may give a frequency
out of the crystal manufacturers specifications. When in
HS mode, the device can have an external clock source
to drive the OSC1/CLKIN pin (Figure 13-2). In this
mode, the oscillator start-up timer is active for a period
of 1024*TOSC. See the PICmicro™ Mid-Range MCU
Reference Manual (DS33023) for details on building an
external oscillator.
Note 1: Higher capacitance increases the stability
of the oscillator, but also increases the start-
up time.
2: Since each resonator/crystal has its own
characteristics, the user should consult the
resonator/crystal manufacturer for appropri-
ate values of external components.
3: Rs may be required in HS mode to avoid
overdriving crystals with low drive level
specification.
4: When migrating from other PICmicro
devices, oscillator performance should be
verified.
FIGURE 13-1: CRYSTAL/CERAMIC
RESONATOR OPERATION
5: Users should consult the USB Specification
1.0 to ensure their resonator/crystal oscilla-
tor meets the required jitter limits for USB
operation.
(HS OSC CONFIGURATION)
OSC1
To internal
logic
C1
13.2.3 H4 MODE
XTAL
OSC2
SLEEP
Rf
In H4 mode, a PLL module is switched on in-line with
the clock provided across OSC1 and OCS2. The output
of the PLL drives FINT.
PIC16C745/765
Rs
C2
Note1
Note 1:
A series resistor may be required for AT strip cut
crystals.
DS41124A-page 96
Advanced Information
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
