MC68HC711xxxx Motorola, MC68HC711xxxx Datasheet - Page 24

• Manufacturer Part Number: MC68HC711xxxx
• Description: Microcontrollers
• Manufacturer: Motorola

General Description
1.4.2 RESET
1.4.3 Crystal Driver and External Clock Input (XTAL and EXTAL)
Data Sheet
24
CAUTION:
A bidirectional control signal, RESET, acts as an input to initialize the MCU to a
known startup state. It also acts as an open-drain output to indicate that an internal
failure has been detected in either the clock monitor or computer operating properly
(COP) watchdog circuit. The CPU distinguishes between internal and external
reset conditions by sensing whether the reset pin rises to a logic 1 in less than two
E-clock cycles after a reset has occurred. See
Do not connect an external resistor capacitor (RC) power-up delay circuit to the
reset pin of M68HC11 devices because the circuit charge time constant can cause
the device to misinterpret the type of reset that occurred.
Because the CPU is not able to fetch and execute instructions properly when V
falls below the minimum operating voltage level, reset must be controlled. A
low-voltage inhibit (LVI) circuit is required primarily for protection of EEPROM
contents. However, since the configuration register (CONFIG) value is read from
the EEPROM, protection is required even if the EEPROM array is not being used.
Presently, there are several economical ways to solve this problem. For example,
two good external components for LVI reset are:
Refer to
These two pins provide the interface for either a crystal or a CMOS- compatible
clock to control the internal clock generator circuitry. The frequency applied to
these pins is four times higher than the desired E-clock rate.
The XTAL pin must be left unterminated when an external CMOS- compatible clock
input is connected to the EXTAL pin. The XTAL output is normally intended to drive
only a crystal. Refer to
1. The Seiko S0854HN (or other S805 series devices):
2. The Motorola MC34064:
a. Extremely low power (2 µA)
a. TO-92 package
a. Limited temperature range, –20°C to +70°C
a. Available in various trip-point voltage ranges
a. TO-92 or SO-8 package
a. Draws about 300 µA
a. Temperature range –40°C to 85°C
a. Well controlled trip point
a. Inexpensive
Section 5. Resets and Interrupts
General Description
Figure 1-9
and
Figure
for further information.
1-10.
Figure 1-7
M68HC11E Family — Rev. 5
and
Figure
1-8.
MOTOROLA
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