NXP Semiconductors freescale MPC5668E, Руководство пользователя, Страница: 13 / 54

MPC5668EVB Users Manual Rev 0.1 May 2009
MPC5668EVBUM/D Page 9 of 29
The MCU clock
control jumpers are
located close to
crystal oscillator
modules.
3.2 MCU Clock Control
3.2.1 Main Clock Selection (J85, J87, J61 and J66)
The EVB supports three possible MCU clock sources:
(1) The local 40MHz ALC pierce oscillator circuit
(2) An oscillator module on the EVB (U20), driving the MCU EXTAL signal
(3) An external clock input to the EVB via the SMA connector (P32), driving the MCU EXTAL signal
The clock circuitry is shown in the diagram below. Please refer to the appropriate daughter card user manual
for specific jumper numbers and circuitry.
Figure 3-5 EVB Clock Selection
Table 3-5 Clock Source Jumper Selection
Jumper Position PCB
Legend Description
J85 (U20 PWR)
FITTED (D) EVB oscillator module U20 is powered
REMOVED EVB oscillator module U20 is not
powered
J87 (OSC SEL)
1-2 (D)
MOD
Daughter card EXT-CLK is routed from
U20
2-3
SMA
Daughter card EXT-CLK is routed from
P32 SMA Connector
J66
Must Match J61 1-2 (D) Y2 MCU Clock is Y2
2-3 GND MCU Clock is Selected by J87
J61
Must Match J66
1-2 (D)
Y2 MCU Clock is Y2
2-3 EVB MCU Clock is Selected by J87
Note that the 3.3V regulator must be enabled when using oscillator module Y1.
CAUTION
The MPC5668 clock circuitry is all 3.3v based. Any external clock signal driven into the SMA connector must
have a maximum voltage of 3.3V.
J85
SMA
(P32)
Oscillator
Module
(U20)
3.3V_SR
Local Crystal
Circuit (Y2)
MCU
EXTAL
XTAL
J87
J66
J61
GND
EVB Clock Circuitry
1
1