cop8cde9 National Semiconductor Corporation, cop8cde9 Datasheet - Page 18

• Manufacturer Part Number: cop8cde9
• Description: 8-bit Cmos Flash Microcontroller With 8k Memory, Virtual Eeprom, 10-bit A/d And Brownout Reset
• Manufacturer: National Semiconductor Corporation

www.national.com
4.0 Functional Description
4.7.1 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 of a
device without the Brownout Reset feature is held low until
the device is within the specified V
on the RESET pin with a delay 5 times (5x) greater than the
power supply rise time 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 .
One exception to the above is that the brownout circuit will
insert a delay of approximately 3 ms on power up or any time
the V
be held in Reset for the duration of this delay before the Idle
WATCHDOG service window bits set and the Clock Moni-
tor bit set. The WATCHDOG and Clock Monitor circuits
are inhibited during reset. The WATCHDOG service win-
dow bits being initialized high default to the maximum
WATCHDOG service window of 64k T0 clock cycles. The
Clock Monitor bit being initialized high will cause a Clock
Monitor error following 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
16–32 T0 clock cycles following the clock frequency
reaching the minimum specified value, at which time the
G1 output will go high.
CC
drops below a voltage of about 1.8V. The device will
CC
voltage. An R/C circuit
FIGURE 10. Brownout Reset Operation
(Continued)
18
4.7.2 On-Chip Brownout Reset
When enabled, the device generates an internal reset as
V
voltage (V
the Idle Timer is preset with 00Fx (240–256 t
reaches a value greater than V
counting down. Upon underflow of the Idle Timer, the internal
reset is released and the device will start executing instruc-
tions. This internal reset will perform the same functions as
external reset. Once V
Timer time-out takes place, instruction execution begins and
the Idle Timer can be used normally. If, however, V
below the selected V
the Idle Timer is preset with 00Fx. The device now waits until
V
When enabled, the functional operation of the device, at
frequency, is guaranteed down to the V
Timer starts counting the 240 to 256 t
soon as the V
mately 1.8V). This behavior is shown in Figure 10 .
CC
CC
FIGURE 9. Reset Circuit Using External Reset
rises. While V
is greater than V
bor
), the device is held in the reset condition and
CC
rises above the trigger voltage (approxi-
CC
bor
CC
is less than the specified brownout
bor
, an internal reset is generated, and
is above the V
and the countdown starts over.
bor
, the Idle Timer starts
C
. This delay starts as
bor
bor
and this initial Idle
level.
20022513
20022512
C
). When V
CC
drops
CC