MC9S12XF512_1 Datasheet, PDF (55/1306 Pages) Freescale Semiconductor, Inc – S12X Microcontrollers

1.2.3 Detailed Signal Descriptions
Chapter 1 MC9S12XF-Family Reference Manual
1.2.4 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 driver output.
1.2.5 RESET — External Reset Pin
The RESET pin is an 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. The RESET pin has an
internal pullup device.
1.2.6 TEST — Test Pin
This input only pin is reserved for test. This pin has a pulldown device.
NOTE
The TEST pin must be tied to VSS in all applications.
1.2.7 BKGD / MODC — Background Debug and Mode Pin
The BKGD/MODC pin is used as a pseudo-open-drain pin for the background debug communication. It
is used as a MCU operating mode select pin during reset. The state of this pin is latched to the MODC bit
at the rising edge of RESET. The BKGD pin has a pullup device.
NOTE
An additional lower-ohm pullup is required as the on-chip pullup device is
not intended to drive the debug line in the case of BDM communication.
1.2.8 Port Pins
1.2.8.1 PAD00 - PAD15 / AN00 - AN15 — Port AD I/0 Pin of ATD
PAD00 - PAD15 are general purpose inputs or outputs and analog inputs AN00 - AN15 of the analog to
digital converter ATD.
1.2.8.2 PA[7:0] / ADDR[15:8] / IVD[15:8] — Port A I/O Pins
PA7-PA0 are general purpose input or output pins. In MCU expanded modes of operation, these pins are
used for the external address bus. In MCU emulation modes of operation, these pins are used for external
address bus and internal visibility read data.
MC9S12XF - Family Reference Manual, Rev.1.19
Freescale Semiconductor
55