MC68HC908AT32 Datasheet, PDF (29/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Pin Assignments
1.4.1 Power Supply Pins (V_DD and V_SS)
V_DD and V_SS are the power supply and ground pins. 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 shown. Place
the C1 bypass capacitor as close to the MCU as possible. Use a high-frequency response ceramic
capacitor for C1. C2 is an optional bulk current bypass capacitor for use in applications that require the
port pins to source high current levels.
MCU
V_DD
V_SS
C1
0.1 µF
+
C2
V_DD
Note: Component values shown represent typical applications.
Figure 1-5. Power Supply Bypassing
V_SS is also the ground for the port output buffers and the ground return for the serial clock in the serial
peripheral interface module (SPI). See Chapter 17 Serial Peripheral Interface Module (SPI).
NOTE
V_SS must be grounded for proper MCU operation.
1.4.2 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).
1.4.3 External Reset Pin (RST)
A logic 0 on the RST pin forces the MCU to a known startup state. RST is bidirectional, allowing a reset
of the entire system. It is driven low when any internal reset source is asserted. See Chapter 7 System
Integration Module (SIM) for more information.
1.4.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. See Chapter 15 External Interrupt (IRQ).
1.4.5 Analog Power Supply Pin (V_DDA)
V_DDA is the power supply pin for the analog portion of the chip. For the MC68HC08AZ32 emulator
protocol, this pin will supply the clock generator module (CGM). However, for the MC68HC08AS20
emulator protocol this pin will supply both the clock generator module and the analog-to-digital converter
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
29