MAC7200 datasheet(117/976 Pages) FREESCALE

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Detailed Signal Descriptions

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

4.3

Detailed Signal Descriptions

4.3.1

EXTAL, XTAL — Oscillator Pins

EXTAL and XTAL are the crystal driver and external clock pins. On reset all the device clocks are derived

from the EXTAL input frequency. XTAL is the crystal output. When the XCLKS pin is driven low, an

external 3.3V clock signal can be driven in on the EXTAL pin directly. Otherwise, the XCLKS pin must

be driven high until after the RESET pin has been negated.

4.3.2

RESET — External Reset Pin

An open drain, active low bidirectional control signal, it acts as an input to initialize the MCU to a known

start-up state, and an output when an internal MCU function causes a Reset. A pull-down resistor can be

activated on this pin. This allows the device to enter reset when the connection to an external reset source

is lost. This resistor is implemented using active elements, and is approximately equivalent to a 20KOhm

resistor under typical operating conditions.

Figure 4-4. Bidirectional Open Drain Pin

4.3.3

XFC — PLL Loop Filter Pin

The XFC pin allows the user to specify the external PLL loop filter components to modify the PLLs

response rate and stability. Please refer to Chapter 23, “Clock and Reset Generator (CRG)” for more

details on this pin and for the calculation of the component values.

Figure 4-5. PLL Loop Filter Connections

VDD

Open Drain

Output Buffer

Input Buffer

MCU

XFC

VDDPLL

MAC7200 Datasheet(PDF) 117 Page - Freescale Semiconductor, Inc