COP820CJ Datasheet, PDF (12/35 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 1k or 2k Memory, Comparator and Brown Out Detector

Reset (Continued)
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 be-
low 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 Volt-
age. If a two pin crystal/resonator clock option is selected,
the Brown Out reset will trigger a 256tc delay. This delay al-
lows the oscillator to stabilize before the device exits the re-
set 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 t_c 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
Port G
Port D
PC
RAM Contents
B, X, SP
PSW, CNTRL1, CNTRL2
and WDREG Registers
Multi-Input Wakeup Registers
WKEDG, WKEN
WKPND
Data and Configuration
Registers for L & G
WATCHDOG Timer
Timer T1 and Accumulator
TRI-STATE
TRI-STATE
HIGH
CLEARED
RANDOM
UNKNOWN
CLEARED
CLEARED
UNKNOWN
CLEARED
Prescalar/Counter each
loaded with FF
Unknown data after
coming out of the HALT
(through Brown Out
Reset) with any Clock
option
Note 8: The development system will detect the BROWN OUT RESET ex-
ternally and will force the RESET pin low. The Development System does not
emulate the 256tc delay.
voltage (Max frequency 4 MHz), For temperature range of
0˚C to 70˚C the Brown Out voltage is expected to be be-
tween 1.9V to 3.9V. The circuit can be enabled or disabled
by Brown Out mask option. If the device is intended to oper-
ate 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 pro-
vided the power supply rise time is slower than 50 µs (0V to
6.0V). Brown Out should not be used at frequencies over 4
MHz (COP840CJ).
Note: Brown Out Circuit is active in HALT mode (with the Brown Out mask
option selected).
Oscillator Circuits
EXTERNAL OSCILLATOR
CKI can be driven by an external clock signal provided it
meets the specified duty cycle, rise and fall times, and input
levels. G7/CKO is available as a general purpose input G7
and/or Halt control.
CRYSTAL OSCILLATOR
By selecting G7/CKO as a clock output, CKI and G7/CKO
can be connected to create a crystal controlled oscillator.
Table 1 shows the component values required for various
standard crystal values.
R/C OSCILLATOR (COP820CJ)
For COP820CJ, selecting CKI as a single pin oscillator, CKI
can make a R/C oscillator. G7/CKO is available as a general
purpose input and/or HALT control. Table 2 shows variation
in the oscillator frequencies as functions of the component
(R and C) values.
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 de-
vice if the operating voltage is below the Brown Out voltage
(between 1.8V to 4.2V at −40˚C to +85˚C). The Minimum op-
erating voltage for the device is 2.5V with Brown Out dis-
abled, but with BROWN OUT enabled the device is guaran-
teed to operate properly down to minimum Brown Out
DS011208-7
FIGURE 5. Clock Oscillator Configurations
R1
(kΩ)
0
0
5.6
R2
(MΩ)
1
1
1
TABLE 1. Crystal Oscillator Configuration
C1
(pF)
30
30
100/200
C2
(pF)
30–36
30–36
100–156
CKI Freq.
(MHz)
10
4
0.455
Conditions
V_CC = 5V
V_CC = 5V
V_CC = 5V
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