PIC16CR58A Microchip Technology, PIC16CR58A Datasheet - Page 41

• Manufacturer Part Number: PIC16CR58A
• Description: ROM-Based 8-Bit CMOS Microcontroller Series
• Manufacturer: Microchip Technology

7.7
The TO and PD bits in the STATUS register can be
tested to determine if a RESET condition has been
caused by a power-up condition, a MCLR or Watchdog
Timer (WDT) reset, or a MCLR or WDT wake-up reset.
TABLE 7-6:
These STATUS bits are only affected by events listed
in Table 7-7.
TABLE 7-7:
Table 7-3 lists the reset conditions for the special
function registers, while Table 7-4 lists the reset
conditions for all the registers.
Legend: u = unchanged
Note 1: The TO and PD bits maintain their status (u) until
Power-up
WDT Time-out
SLEEP instruction
CLRWDT instruction
Legend: u = unchanged
TO
1998 Microchip Technology Inc.
1
u
1
0
0
Note:
Event
Time-Out Sequence and Power Down
Status Bits (TO/PD)
PD
does not change the TO and PD status bits.
a reset occurs. A low-pulse on the MCLR input
1
u
0
1
0
A WDT time-out will occur regardless of
the status of the TO bit. A SLEEP instruc-
tion will be executed, regardless of the sta-
tus of the PD bit.
Power-up (POR)
MCLR reset (normal operation)
MCLR wake-up reset (from SLEEP)
WDT reset (normal operation)
WDT wake-up reset (from SLEEP)
TO/PD STATUS AFTER
RESET
EVENTS AFFECTING TO/PD
STATUS BITS
RESET was caused by
TO
1
0
1
1
PD
1
u
0
1
No effect on PD
Remarks
(1)
Preliminary
7.8
A brown-out is a condition where device power (V
dips below its minimum value, but not to zero, and then
recovers. The device should be reset in the event of a
brown-out.
To reset PIC16C5X devices when a brown-out occurs,
external brown-out protection circuits may be built, as
shown in Figure 7-14 and Figure 7-15.
FIGURE 7-14: BROWN-OUT PROTECTION
FIGURE 7-15: BROWN-OUT PROTECTION
This circuit will activate reset when V
0.7V (where Vz = Zener voltage).
This brown-out circuit is less expensive, although
less accurate. Transistor Q1 turns off when V
is below a certain level such that:
33k
V
Reset on Brown-Out
DD
R1
R2
V
DD
V
10k
DD
CIRCUIT 1
CIRCUIT 2
•
R1 + R2
Q1
40k
R1
PIC16C5X
Q1
40k
MCLR
PIC16C5X
V
DD
DD
= 0.7V
MCLR
PIC16C5X
V
DS30453B-page 41
DD
goes below Vz +
DD
DD
)