MC68HC711PH8 Motorola, MC68HC711PH8 Datasheet - Page 29

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MC68HC711PH8

Manufacturer Part Number
MC68HC711PH8
Description
High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit
Manufacturer
Motorola
Datasheet
2.2
An active low bidirectional control signal, RESET, acts as an input to initialize the MCU to a known
start-up state. It also acts as an open-drain output to indicate that an internal failure has been
detected in either the clock monitor or the COP watchdog circuit. The CPU distinguishes between
internal and external reset conditions by sensing whether the reset pin rises to a logic one in less
than four E clock cycles after an internal reset has been released. It is therefore not advisable to
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. Refer to Section 10 for further information.
Figure 2-3 illustrates a typical reset circuit that includes an external switch together with a low
voltage inhibit circuit, to prevent power transitions, or RAM or EEPROM corruption.
2.3
These two pins provide the interface for either a crystal or a CMOS compatible clock to control the
internal clock generator circuitry. If the PLL circuit is not being used to provide the E clock, the
frequency applied to these pins must be four times higher than the desired E clock rate. Figure 2-4
shows oscillator connections that should be used when the PLL is disabled, and Figure 2-5 shows the
connections that should be used when the PLL is enabled.
MC68HC11PH8
RESET
Crystal driver and external clock input (XTAL, EXTAL)
Manual
reset
4.7 k
Figure 2-3 External reset circuitry
V
DD
4.7 k
PIN DESCRIPTIONS
1 F
MC34064
MC34164
GND
GND
V
IN
IN
DD
2
3
2
3
RESET
RESET
1
1
V
DD
4.7 k
To M68HC11
RESET
MOTOROLA
TPG
2-3
2

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