General Description
MC68HC08KH12A Data Sheet, Rev. 1.1
20
Freescale Semiconductor
1.4.3 Power Supply Pins (V
DDA
, V
SSA
, V
DD1
, V
SS1
, V
DD2
, and V
SS2
)
V
DDA
and V
SSA
are the analog power supply and ground pins used by the on-chip Phase-Locked Loop
circuit.
V
DD2
and V
SS2
are the power supply and ground pins used by the internal circuitry of the chip.
V
DD1
and V
SS1
are the power supply and ground pins to the I/O pads. The MCU operates from a single
power supply.
Fast signal transitions on MCU pins place high, short-duration current demands on the power supply. To
prevent noise problems, take special care to provide power supply bypassing at the MCU as
Figure 1-4
shows. Place the bypass capacitors as close to the MCU power pins as possible. Use
high-frequency-response ceramic capacitors for C
BYPASS
. C
BULK
are optional bulk current bypass
capacitors for use in applications that require the port pins to source high current levels.
Figure 1-4. Power Supply Bypassing
1.4.4 Oscillator Pins (OSC1 and OSC2)
The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. (See
Chapter 8 Clock
Generator Module (CGM)
.)
1.4.5 External Reset Pin (RST)
A logic zero on the RST pin forces the MCU to a known start-up state. RST is bidirectional, allowing a
reset of the entire system. It is driven low when any internal reset source is asserted. The RST pin
contains an internal pullup device. ((See
Chapter 7 System Integration Module (SIM)
.)
1.4.6 External Interrupt Pin (IRQ1)
IRQ1 is an asynchronous external interrupt pin. This pin contains an internal pullup device.
(See
Chapter 14 External Interrupt (IRQ)
.)
MCU
C
BULK
C
BYPASS
10nF
V
SS1
+
NOTE: Values shown are typical values.
V
DD2
C
BYPASS
10nF
V
DD2
C
BYPASS
10nF
V
SS2
V
SSA
V
DDA
Vbus