Datasheet

 2010 Microchip Technology Inc. DS70138G-page 151
dsPIC30F3014/4013
20.4 Reset
The dsPIC30F3014/4013 differentiates between
various kinds of Reset:
a) Power-on Reset (POR)
b) MCLR
Reset during normal operation
c) MCLR
Reset during Sleep
d) Watchdog Timer (WDT) Reset (during normal
operation)
e) Programmable Brown-out Reset (BOR)
f) RESET Instruction
g) Reset caused by trap lockup (TRAPR)
h) Reset caused by illegal opcode or by using an
uninitialized W register as an Address Pointer
(IOPUWR)
Different registers are affected in different ways by var-
ious Reset conditions. Most registers are not affected
by a WDT wake-up since this is viewed as the resump-
tion of normal operation. Status bits from the RCON
register are set or cleared differently in different Reset
situations, as indicated in Table 20-5. These bits are
used in software to determine the nature of the Reset.
A block diagram of the On-Chip Reset Circuit is shown
in Figure 20-2.
A MCLR
noise filter is provided in the MCLR Reset
path. The filter detects and ignores small pulses.
Internally generated Resets do not drive MCLR pin low.
FIGURE 20-2: RESET SYSTEM BLOCK DIAGRAM
20.4.1 POR: POWER-ON RESET
A power-on event generates an internal POR pulse
when a V
DD rise is detected. The Reset pulse occurs at
the POR circuit threshold voltage (V
POR) which is nom-
inally 1.85V. The device supply voltage characteristics
must meet specified starting voltage and rise rate
requirements. The POR pulse resets a POR timer and
places the device in the Reset state. The POR also
selects the device clock source identified by the
oscillator configuration fuses.
The POR circuit inserts a small delay, T
POR, which is
nominally 10 s and ensures that the device bias
circuits are stable. Furthermore, a user-selected
power-up time-out (T
PWRT) is applied. The TPWRT
parameter is based on device Configuration bits and
can be 0 ms (no delay), 4 ms, 16 ms, or 64 ms. The
total delay is at device power-up, T
POR + TPWRT. When
these delays have expired, SYSRST
is negated on the
next leading edge of the Q1 clock and the PC jumps to
the Reset vector.
The timing for the SYSRST
signal is shown in
Figure 20-3 through Figure 20-5.
S
R
Q
MCLR
VDD
VDD Rise
Detect
POR
SYSRST
Sleep or Idle
Brown-out
Reset
BOREN
RESET
Instruction
WDT
Module
Digital
Glitch Filter
BOR
Trap Conflict
Illegal Opcode/
Uninitialized W Register