cop8sgr5vej8xxx National Semiconductor Corporation, cop8sgr5vej8xxx Datasheet - Page 19

• Manufacturer Part Number: cop8sgr5vej8xxx
• Description: 8-bit Cmos Rom Based And Otp Microcontrollers With 8k To 32k Memory, Two Comparators And Usart
• Manufacturer: National Semiconductor Corporation

5.0 Functional Description
DOG logic and the Clock Monitor detector armed, with the
WATCHDOG service window bits set and the Clock Monitor
bit set. The WATCHDOG and Clock Monitor circuits are
inhibited during reset. The WATCHDOG service window bits
being initialized high default to the maximum WATCHDOG
service window of 64k t
being initialized high will cause a Clock Monitor error follow-
ing reset if the clock has not reached the minimum specified
frequency at the termination of reset. A Clock Monitor error
will cause an active low error output on pin G1. This error
output will continue until 16 t
the clock frequency reaching the minimum specified value,
at which time the G1 output will go high.
5.9.1 External Reset
The RESET input when pulled low initializes the device. The
RESET pin must be held low for a minimum of one instruc-
tion cycle to guarantee a valid reset. During Power-Up ini-
tialization, the user must ensure that the RESET pin is held
low until the device is within the specified V
R/C circuit on the RESET pin with a delay 5 times (5x)
greater than the power supply rise time or 15 µs whichever is
greater, is recommended. Reset should also be wide enough
to ensure crystal start-up upon Power-Up.
RESET may also be used to cause an exit from the HALT
mode.
A recommended reset circuit for this device is shown in
Figure 9 .
RC
5.9.2 On-Chip Power-On Reset
The on-chip reset circuit is selected by a bit in the ECON
register. When enabled, the device generates an internal
reset as V
reset circuitry is able to detect both fast and slow rise times
on V
antee an on-chip power-on-reset, V
less than the start voltage specified in the DC characteris-
tics. Also, if V
powering back up to the operating range. If this is not pos-
sible, it is recommended that external reset be used.
Under no circumstances should the RESET pin be allowed
to float. If the on-chip Power-On Reset feature is being used,
>
The device comes out of reset with both the WATCH-
5x power supply rise time or 15 µs, whichever is greater.
CC
FIGURE 9. Reset Circuit Using External Reset
(V
CC
CC
rises to a voltage level above 2.0V. The on-chip
rise time between 10 ns and 50 ms).To guar-
CC
be lowered to the start voltage before
C
clock cycles. The Clock Monitor bit
C
–32 t
CC
C
must start at a voltage
clock cycles following
10131714
CC
(Continued)
voltage. An
19
RESET pin should be connected directly, or through a
pull-up resistor, to V
detector will always preset the Idle timer to 0FFF(4096 t
At this time, the internal reset will be generated.
If the Power-On Reset feature is enabled, the internal reset
will not be turned off until the Idle timer underflows. The
internal reset will perform the same functions as external
reset. The user is responsible for ensuring that V
minimum level for the operating frequency within the 4096
t
additional internal resets occur as long as V
above 2.0V.
The contents of data registers and RAM are unknown fol-
lowing the on-chip reset.
C
FIGURE 10. Reset Timing (Power-On Reset Enabled)
. After the underflow, the logic is designed such that no
FIGURE 11. Reset Circuit Using Power-On Reset
with V
CC
. The output of the power-on reset
CC
Tied to RESET
10131716
CC
www.national.com
CC
10131715
is at the
remains
C
).