COPCH823CJ Datasheet, PDF (8/32 Pages) National Semiconductor (TI) – 8-bit Microcontroller with with Multi-Input Wake Up and Brown Detecter

Functional Description (Continued)
If the external or RC Clock option is being used
RAM Contents
UNCHANGED
Timer T1 and A Contents
UNCHANGED
WATCHDOG Timer Prescaler Counter ALTERED
The external RESET takes priority over the Brown Out Re-
set
Note
If the RESET pin is pulled low while Brown Out occurs (Brown Out
circuit has detected Brown Out condition) the external reset will not
occur until the Brown Out condition is removed External reset has
priority only if V_CC is greater than the Brown Out voltage
RC l 5 c Power Supply Rise Time
TL DD 11208–6
FIGURE 4 Recommended Reset Circuit
WATCHDOG RESET
With WATCHDOG enabled the WATCHDOG logic resets
the device if the user program does not service the WATCH-
DOG timer within the selected service window The
WATCHDOG reset does not disable the WATCHDOG
Upon WATCHDOG reset the WATCHDOG Prescaler
Counter are each initialized with FF Hex
The following actions occur upon WATCHDOG reset that
are different from external reset
WDREN WATCHDOG Reset Enable bit UNCHANGED
WDUDF WATCHDOG Underflow bit
UNCHANGED
Additional initialization actions that occur as a result of
WATCHDOG reset are as follows
Port L
TRI-STATE
Port G
TRI-STATE
Port D
HIGH
PC
CLEARED
Ram Contents
UNCHANGED
B X SP
UNCHANGED
PSW CNTRL1 and CNTRL2 (except
WDUDF Bit) Registers
CLEARED
Multi-Input Wakeup Registers
WKEDG WKEN
WKPND
CLEARED
UNKNOWN
Data and Configuration
Registers for L G
CLEARED
WATCHDOG Timer
Prescalar Counter
each loaded with FF
BROWN OUT RESET
The on-board Brown Out protection circuit resets the device
when the operating voltage (V_CC) is lower than the Brown
Out voltage The device is held in reset when V_CC stays
below the Brown Out Voltage The device will remain in
RESET as long as V_CC is below the Brown Out Voltage The
Device will resume execution if V_CC rises above the Brown
Out Voltage If a two pin crystal resonator clock option is
selected the Brown Out reset will trigger a 256tc delay This
delay allows the oscillator to stabilize before the device ex-
its the reset state The delay is not used if the clock option is
either R C or external clock The contents of data registers
and RAM are unknown following a Brown Out reset The
external reset takes priority over Brown Out Reset and will
deactivate the 256 tc cycles delay if in progress The Brown
Out reset takes priority over the WATCHDOG reset
The following actions occur as a result of Brown Out reset
Port L
TRI-STATE
Port G
TRI-STATE
Port D
HIGH
PC
CLEARED
RAM Contents
RANDOM
B X SP
UNKNOWN
PSW CNTRL1 CNTRL2
and WDREG Registers
CLEARED
Multi-Input Wakeup Registers
WKEDG WKEN
WKPND
CLEARED
UNKNOWN
Data and Configuration
Registers for L G
CLEARED
WATCHDOG Timer
Prescalar Counter each
loaded with FF
Timer T1 and Accumulator
Unknown data after
coming out of the HALT
(through Brown Out
Reset) with any Clock
option
Note The development system will detect the BROWN OUT RESET exter-
nally and will force the RESET pin low The Development System
does not emulate the 256tc delay
Brown Out Detection
An on-board detection circuit monitors the operating voltage
(V_CC) and compares it with the minimum operating voltage
specified The Brown Out circuit is designed to reset the
device if the operating voltage is below the Brown Out volt-
age (between 1 8V to 4 2V at b40 C to a85 C) The Mini-
mum operating voltage for the device is 2 5V with Brown
Out disabled but with BROWN OUT enabled the device is
guaranteed to operate properly down to minimum Brown
Out voltage (Max frequency 4 MHz) For temperature range
of 0 C to 70 C the Brown Out voltage is expected to be
between 1 9V to 3 9V The circuit can be enabled or dis-
abled by Brown Out mask option If the device is intended to
operate at lower V_CC (lower than Brown Out voltage VBO
max) the Brown Out circuit should be disabled by the mask
option
The Brown Out circuit may be used as a power-up reset
provided the power supply rise time is slower than 50 ms (0V
to 6 0V)
Note Brown Out Circuit is active in HALT mode (with the Brown Out mask
option selected)
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