Pin Descriptions
M68HC11E Family Data Sheet, Rev. 5.1
Freescale Semiconductor
21
1.4.1 VDD and VSS
Power is supplied to the MCU through VDD and VSS. VDD is the power supply, VSS is ground. The MCU
operates from a single 5-volt (nominal) power supply. Low-voltage devices in the E series operate at
3.0–5.5 volts.
Very fast signal transitions occur on the MCU pins. The short rise and fall times place high, short duration
current demands on the power supply. To prevent noise problems, provide good power supply bypassing
at the MCU. Also, use bypass capacitors that have good
high-frequency characteristics and situate them as close to the MCU as possible. Bypass requirements
vary, depending on how heavily the MCU pins are loaded.
Figure 1-7. External Reset Circuit
Figure 1-8. External Reset Circuit with Delay
4.7 k
TO RESET
VDD
MC34(0/1)64
RESET
GND
IN
OF M68HC11
2
1
3
VDD
TO RESET
VDD
MC34064
RESET
GND
IN
OF M68HC11
RESET
GND
IN
MANUAL
RESET SWITCH
4.7 k
1.0
F
MC34164
4.7 k
VDD
OPTIONAL POWER-ON DELAY AND MANUAL RESET SWITCH
4.7 k