Clock Source Select Header (J2); Keep Alive Power 2 Select Header (J3) - Motorola MPC505EVB User Manual

HARDWARE PREPARATION AND INSTALLATION
2.2.2

Clock Source Select Header (J2)

Use jumper header J2 to select either a crystal or clock oscillator as the MCU clock source. The
drawing below shows the factory configuration: bus wire soldered on pins 2 and 3. This
configuration selects the crystal clock source; crystal in socket at located Y1. When you want to
use the clock oscillator as the EVB clock, move the bus wire on J2 from pins 2 and 3 to pins 1
and 2 and remove the bus wire on J1 (see paragraph 2.2.1). This disconnects the MCU XTAL pin
from the crystal clock circuit at location Y1 and selects the crystal oscillator (U7) as the MCU
clock source. The frequency of the crystal clock circuit is 4 MHz. The frequency of the crystal
oscillator circuit can be as fast as 40 MHz.
2.2.3

Keep Alive Power 2 Select Header (J3)

Jumper header J3 provides power to the MCU-internal RAM module via the MCU VKAPWR2
pin. You may use either the on-board +3.3 Vdc (jumper on J3 pins 1 and 2) or connect an
external +3.3 Vdc power supply to J3 pins 2 and 3. An external +3.3 Vdc power supply on J3
pins 2 and 3 will maintain MCU-internal RAM data after EVB power is turned OFF. To attach
an external power supply to VKAPWR2: remove the jumper on J3 pins 1 and 2, and connect the
power supply ground to J3 pin 3 and +3.3 Vdc to pin 2.
Applying power to the EVB with J4 removed and no external
power supply attached to J4 will damage the MPC505 MCU.
Always keep a jumper or an external +3.3 Vdc power supply on J4
pins 1 and 2. If using an external power supply, apply VKAPWR1
before powering up the EVB.
2-6
Bus Wire
J2
3 2 1
CAUTION
MPC505EVBUM/D