cop8tab9 National Semiconductor Corporation, cop8tab9 Datasheet - Page 18

• Manufacturer Part Number: cop8tab9
• Description: 8-bit Cmos Flash Microcontroller With 2k Byte Or 4k Byte Memory
• Manufacturer: National Semiconductor Corporation

www.national.com
10.0 Functional Description
10.6.1 External Reset
The RESET input, when pulled low, initializes the device.
The RESET pin must be held low for a minimum of one
instruction cycle to guarantee a valid reset. An R/C circuit on
the RESET pin with a delay 5 times (5x) greater than the
power supply rise time is recommended. Reset should also
be long enough to ensure crystal start-up upon Power-Up.
RESET may also be used to cause an exit from the HALT
mode.
Note: Flash memory may be non-volatile, but it is not invulnerable. Any
A recommended reset circuit for this device is shown in
Figure 11 .
10.6.2 On-Chip Power-On Reset
The device generates an internal reset as V
voltage level above 2.0V. The on-chip reset circuitry is able
to detect both fast and slow rise times on V
between 20 µs and 10 ms).
Under no circumstances should the RESET pin be allowed
to float. If the on-chip Power-On Reset feature is being used,
RESET pin should be connected to V
through a pull-up resistor. If forced operation from the Boot
ROM is anticipated, a pull-up resistor should always be used
so that the ISP circuit can override the RESET circuit and
force the RESET pin low. The output of the power-on reset
detector will always preset the Idle timer to 00FF(256 t
this time, the internal reset will be generated.
The internal reset will not be turned off until the Idle timer
underflows. The internal reset will perform the same func-
tions as external reset. The user is responsible for ensuring
that V
(Continued)
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 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.
FIGURE 11. Reset Circuit Using External Reset
controller which features the capability for the software to modify the
contents of the Flash memory is susceptible to inadvertent writes or
erases any time V
conditions, the clock is running and the device is not held in Reset. For
this reason, we recommend the use of external brownout detection
any time V
operating conditions.
CC
is at the minimum level for operating within the 256
CC
drops below the minimum guaranteed V
CC
is below the minimum guaranteed operating
CC
, either directly or
CC
(V
CC
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CC
CC
rises to a
/Frequency
rise time
C
). At
18
t
Power On Reset circuit will generate no additional internal
resets as long as V
Note: The POR feature of the COP8TAB9/TAC9 is not intended to function as
The contents of data registers and RAM are unknown fol-
lowing the on-chip reset.
10.7 OSCILLATOR CIRCUITS
There are five clock oscillator options available: fully internal
R/C Oscillator, R/C Oscillator with external frequency deter-
mination resistor, Crystal Oscillator with or without on-chip
bias resistor and External Oscillator. The oscillator feature is
selected by programming the Option Byte, which is summa-
rized in Table 2 .
C
FIGURE 12. Reset Timing (Power-On Reset Enabled)
Option
. After the underflow, the logic is designed such that the
Bit 6
0
0
0
0
1
a brownout detector. A brownout condition is reached whenever VCC
of the device goes below the minimum guaranteed operating condi-
tions. The minimum guaranteed operating conditions are defined in the
Electrical Specifications. We strongly recommend the use of an exter-
nal supervisory circuit which ensures that the COP8 device is held in
the RESET state until Vcc has recovered to the minimum operating
conditions as stated above.
Option
Bit 4
0
0
1
1
x
TABLE 2. Oscillator Option
with V
Option
CC
Bit 3
0
1
0
1
x
remains above 2.0V.
CC
On-Chip R/C Oscillator
R/C Oscillator with External Resistor
Crystal Oscillator with Internal Bias
Resistor
Crystal Oscillator with External Bias
Resistor
External Oscillator
Tied to RESET
Oscillator Option
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