PIC17C756A MICROCHIP [Microchip Technology], PIC17C756A Datasheet - Page 20

• Manufacturer Part Number: PIC17C756A
• Description: High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC17C7XX
4.1.6
For timing insensitive applications, the RC device
option offers additional cost savings. RC oscillator fre-
quency is a function of the supply voltage, the resistor
(R
temperature. In addition to this, oscillator frequency will
vary from unit to unit due to normal process parameter
variation. Furthermore, the difference in lead frame
capacitance between package types will also affect
oscillation frequency, especially for low C
The user also needs to take into account variation due
to tolerance of external R and C components used.
Figure 4-7 shows how the R/C combination is con-
nected to the PIC17CXXX. For R
2.2 k , the oscillator operation may become unstable,
or stop completely. For very high R
1 M ), the oscillator becomes sensitive to noise,
humidity and leakage. Thus, we recommend to keep
R
Although the oscillator will operate with no external
capacitor (C
above 20 pF for noise and stability reasons. With little
or no external capacitance, oscillation frequency can
vary dramatically due to changes in external capaci-
tances, such as PCB trace capacitance or package
lead frame capacitance.
See Section 21.0 for RC frequency variation from part
to part due to normal process variation. The variation is
larger for larger R (since leakage current variation will
affect RC frequency more for large R) and for smaller
C (since variation of input capacitance will affect RC
frequency more).
See Section 21.0 for variation of oscillator frequency
due to V
quency variation due to operating temperature for
given R, C, and V
The oscillator frequency, divided by 4, is available on
the OSC2/CLKOUT pin and can be used for test pur-
poses or to synchronize other logic (see Figure 4-8 for
waveform).
DS30289B-page 20
EXT
EXT
) and capacitor (C
between 3 k and 100 k .
DD
for given R
RC OSCILLATOR
EXT
= 0 pF), we recommend using values
DD
values.
EXT
EXT
/C
) values, and the operating
EXT
values, as well as fre-
EXT
EXT
values below
values (e.g.
EXT
values.
FIGURE 4-7:
4.1.6.1
As the device voltage increases, the RC will immedi-
ately start its oscillations once the pin voltage levels
meet the input threshold specifications (parameter
#D032 and parameter #D042 in the electrical specifica-
tion section). The time required for the RC to start oscil-
lating depends on many factors. These include:
• Resistor value used
• Capacitor value used
• Device V
• System temperature
C
V
R
EXT
SS
EXT
V
DD
DD
RC Start-up
rise time
F
OSC
/4
RC OSCILLATOR MODE
OSC2/CLKOUT
OSC1
2000 Microchip Technology Inc.
PIC17CXXX
Internal
Clock