PIC16F946 Datasheet, PDF (77/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

4.3.2 EC MODE
The External Clock (EC) mode allows an externally
generated logic level as the system clock source.
When operating in this mode, an external clock source
is connected to the OSC1 pin and the RA6 pin is
available for general purpose I/O. Figure 4-2 shows the
pin connections for EC mode.
The Oscillator Start-up Timer (OST) is disabled when
EC mode is selected. Therefore, there is no delay in
operation after a Power-on Reset (POR) or wake-up
from Sleep. Because the PIC16F946 design is fully
static, stopping the external clock input will have the
effect of halting the device while leaving all data intact.
Upon restarting the external clock, the device will
resume operation as if no time had elapsed.
FIGURE 4-2:
EXTERNAL CLOCK (EC)
MODE OPERATION
Clock
(External
System)
RA6
PIC16F946
OSC1/
CLKIN
FOSC _Internal
Clock
FOSC<2:0> = 011
RA6/OSC2/CLKO/T1OSO
PIC16F946
4.3.3 LP, XT, HS MODES
The LP, XT and HS modes support the use of quartz
crystal resonators or ceramic resonators connected to
the OSC1 and OSC2 pins (Figures 4-3 and 4-4). The
mode selects a low, medium or high gain setting of the
internal inverter-amplifier to support various resonator
types and speed.
LP Oscillator mode selects the lowest gain setting of the
internal inverter-amplifier. LP mode current consumption
is the least of the three modes. This mode is best suited
to drive resonators with a low drive level specification, for
example, tuning fork type crystals.
Note:
In the past, the sources for the LP oscilla-
tor and Timer1 oscillator have been sepa-
rate circuits. In this family of devices, the
LP oscillator and Timer1 oscillator use the
same oscillator circuitry. When using a
device configured for the LP oscillator and
with T1OSCEN = 1, the source of the
clock for each function comes from the
same oscillator block.
XT Oscillator mode selects the intermediate gain
setting of the internal inverter-amplifier. XT mode
current consumption is the medium of the three modes.
This mode is best suited to drive resonators with a
medium drive level specification, for example,
low-frequency/AT-cut quartz crystal resonators.
HS Oscillator mode selects the highest gain setting of
the internal inverter-amplifier. HS mode current
consumption is the highest of the three modes. This
mode is best suited for resonators that require a high
drive setting, for example, high-frequency/AT-cut
quartz crystal resonators or ceramic resonators.
Figures 4-3 and 4-4 show typical circuits for quartz
crystal and ceramic resonators, respectively.
© 2005 Microchip Technology Inc.
Preliminary
DS41265A-page 75