MC9S08GT16 MOTOROLA [Motorola, Inc], MC9S08GT16 Datasheet - Page 28

• Manufacturer Part Number: MC9S08GT16
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Chapter 2 Pins and Connections
2.3.1
V
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 close to the MCU power pins as
practical to suppress high-frequency noise.
V
the ATD. A 0.1-µF ceramic bypass capacitor should be located as close to the MCU power pins as practical
to suppress high-frequency noise.
2.3.2
Out of reset, the MCU uses an internally generated clock (self-clocked mode — f
approximately equivalent to an 8-MHz crystal rate. This frequency source is used during reset startup and
can be enabled as the clock source for stop recovery to avoid the need for a long crystal startup delay. This
MCU also contains a trimmable internal clock generator (ICG) module that can be used to run the MCU.
For more information on the ICG, see
The oscillator in this MCU is a Pierce oscillator that can accommodate a crystal or ceramic resonator in
either of two frequency ranges selected by the RANGE bit in the ICGC1 register. Rather than a crystal or
ceramic resonator, an external oscillator can be connected to the EXTAL input pin, and the XTAL output
pin can be used as general I/O.
Refer to
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.
R
value is not generally critical. Typical systems use 1 MΩ 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 sizing 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).
2.3.3
RESET is a dedicated pin with a pullup 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
28
F
DD
DDAD
is used to provide a bias path to keep the EXTAL input in its linear range during crystal startup and its
and V
and V
Figure 2-5
Power
Oscillator
Reset
SS
SSAD
are the primary power supply pins for the MCU. This voltage source supplies power to all
are the analog power supply pins for the MCU. This voltage source supplies power to
for the following discussion. R
MC9S08GB/GT Data Sheet, Rev. 2.3
Chapter 7, “Internal Clock Generator (ICG)
S
(when used) and R
F
should be low-inductance
Self_reset
Module.”
Freescale Semiconductor
) that is