Datasheet

PIC16C62B/72A
 1998-2013 Microchip Technology Inc. Preliminary DS35008C-page 57
10.2.3 RC OSCILLATOR
For timing insensitive applications, the “RC” device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the resis-
tor (R
EXT) and capacitor (CEXT) values, and the operat-
ing temperature. In addition to this, the oscillator
frequency will vary from unit to unit due to normal pro-
cess parameter variation. Furthermore, the difference
in lead frame capacitance between package types will
also affect the oscillation frequency, especially for low
C
EXT values. The user also needs to take into account
variation due to tolerance of external R and C compo-
nents used. Figure 10-4 shows how the R/C combina-
tion is connected to the PIC16CXXX.
FIGURE 10-4: RC OSCILLATOR MODE
10.3 Reset
The PIC16CXXX differentiates between various kinds
of reset:
• Power-on Reset (POR)
•MCLR
reset during normal operation
•MCLR reset during SLEEP
• WDT Reset (during normal operation)
• WDT Wake-up (during SLEEP)
• Brown-out Reset (BOR)
Some registers are not affected in any reset condition;
their status is unknown on POR and unchanged by any
other reset. Most other registers are reset to a “reset
state” on Power-on Reset (POR), on the MCLR
and
WDT Reset, on MCLR
reset during SLEEP, and on
Brown-out Reset (BOR). They are not affected by a
WDT Wake-up from SLEEP, which is viewed as the
resumption of normal operation. The TO
and PD bits
are set or cleared depending on the reset situation, as
indicated in Table 10-4. These bits are used in software
to determine the nature of the reset. See Table 10-6 for
a full description of reset states of all registers.
A simplified block diagram of the on-chip reset circuit is
shown in Figure 10-5.
The PIC devices have a MCLR
noise filter in the MCLR
reset path. The filter will ignore small pulses. However,
a valid MCLR
pulse must meet the minimum pulse
width (TmcL, Specification #30).
No internal reset source (WDT, BOR, POR) willdrive
the MCLR
pin low.
OSC2/CLKOUT
Cext
Rext
PIC16CXX
OSC1
Fosc/4
Internal
clock
VDD
VSS
Recommended values: 3 k  Rext  100 k
Cext > 20pF