MC9S08DN60F1CLF datasheet(27/356 Pages) FREESCALE

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Chapter 2 Pins and Connections

MC9S08DN60 Series Data Sheet, Rev 3

Freescale Semiconductor

2.2.1

Power

VDD and VSS are the primary power supply pins for the MCU. This voltage source supplies power to all

I/O buffer circuitry and to an internal voltage regulator. The internal voltage regulator provides regulated

lower-voltage source to the CPU and other internal circuitry of the MCU.

Typically, application systems have two separate capacitors across the power pins. In this case, there

should be a bulk electrolytic capacitor, such as a 10-

μF tantalum capacitor, to provide bulk charge storage

for the overall system and a 0.1-

μF ceramic bypass capacitor located as near to the MCU power pins as

practical to suppress high-frequency noise. The MC9S08DN60 Series has two VDD pins except on the

32-pin package. Each pin must have a bypass capacitor for best noise suppression.

VDDA and VSSA are the analog power supply pins for the MCU. This voltage source supplies power to the

ADC module. A 0.1-

μF ceramic bypass capacitor should be located as near to the MCU power pins as

practical to suppress high-frequency noise.

2.2.2

Oscillator

Immediately after reset, the MCU uses an internally generated clock provided by the multi-purpose clock

generator (MCG) module. For more information on the MCG, see Chapter 8, “Multi-Purpose Clock

Generator (S08MCGV1).”

The oscillator (XOSC) in this MCU is a Pierce oscillator that can accommodate a crystal or ceramic

resonator. Rather than a crystal or ceramic resonator, an external oscillator can be connected to the EXTAL

input pin.

Refer to Figure 2-4 for the following discussion. RS (when used) and RF should be low-inductance

resistors such as carbon composition resistors. Wire-wound resistors and some metal ﬁlm resistors have

too much inductance. C1 and C2 normally should be high-quality ceramic capacitors that are speciﬁcally

designed for high-frequency applications.

RF is used to provide a bias path to keep the EXTAL input in its linear range during crystal startup; its value

is not generally critical. Typical systems use 1 M

Ω to 10 MΩ. Higher values are sensitive to humidity, and

lower values reduce gain and (in extreme cases) could prevent startup.

C1 and C2 are typically in the 5-pF to 25-pF range and are chosen to match the requirements of a speciﬁc

crystal or resonator. Be sure to take into account printed circuit board (PCB) capacitance and MCU pin

capacitance when selecting C1 and C2. The crystal manufacturer typically speciﬁes a load capacitance

which is the series combination of C1 and C2 (which are usually the same size). As a ﬁrst-order

approximation, use 10 pF as an estimate of combined pin and PCB capacitance for each oscillator pin

(EXTAL and XTAL).

2.2.3

RESET

RESET is a dedicated pin with a pull-up device built in. It has input hysteresis, a high current output driver,

and no output slew rate control. Internal power-on reset and low-voltage reset circuitry typically make

external reset circuitry unnecessary. This pin is normally connected to the standard 6-pin background

debug connector so a development system can directly reset the MCU system. If desired, a manual external

reset can be added by supplying a simple switch to ground (pull reset pin low to force a reset).

MC9S08DN60F1CLF Datasheet(PDF) 27 Page - Freescale Semiconductor, Inc

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