HCS08 datasheet(30/374 Pages) NXP

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Chapter 2 Pins and Connections

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

2.3.1

Power (VDD, VSS, VSSOSC, VDDAD, VSSAD, VUSB33)

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 must

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 paired VDD and VSS power

pins as practical to suppress high-frequency noise. The MC9S08JM60 series have a VSSOSC pin. This pin

must be connected to the system ground plane or to the primary VSS pin through a low-impedance

connection.

VDDAD and VSSAD 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 must be located as near to the analog power pins as

practical to suppress high-frequency noise.

VUSB33 is connected to the internal USB 3.3-V regulator. VUSB33 maintains an output voltage of 3.3 V and

can only source enough current for internal USB transceiver and USB pullup resistor. Two separate

capacitors (4.7-

μF bulk electrolytic stability capacitor and 0.47-μF ceramic bypass capacitors) must be

connected across this pin to ground to decrease the output ripple of this voltage regulator when it is

enabled.

2.3.2

Oscillator (XTAL, EXTAL)

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 12, “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.

RS (when used) and RF must 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 must

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).

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