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2.2.1
Crystal Clock Select Header (J1)
Jumper header J1 connects the crystal clock to the MCU XTAL pin clock source. The drawing
below shows the factory configuration: bus wire soldered on pins 1 and 2. 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, remove the bus wire on J1 and move the bus wire on J2 from pins 2
and 3 to pins 1 and 2 (see paragraph 2.2.2). This disconnects the MCU XTAL pin from the
crystal clock circuit at location Y1 and selects the clock 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.
The EVB comes with a 4 MHz crystal and a socket for a crystal oscillator. The EVB is factory
configured to use the 4 MHz crystal as the input. You can configure the clock frequency up to 33
MHz by setting the MF bits (bits 9-12) and RFD bits (bits 28-31) in register SCCR at address
0x8007_FC50 (shown in Table 2-3).
Table 2-3. MF and RFD Bits Required to Set Clock Speed
RFD [0:3]
MF=
X000
(X4)
0 = 0000
16
1 = 0001
8
2 = 0010
4
3 = 0011
2
4 = 0100
1
5 = 0101
.5
6 = 0110
.25
7 = 0111
.125
MPC505EVBUM/D
J1
2
1
CLKOUT (megahertz)
MF=
MF=
MF=
X001
X010
X011
(X5)
(X6)
(X7)
20
24
10
12
5
6
2
2.5
3
3.5
1.25
1.5
1.75
.625
.75
.875
.313
.375
.438
.156
.188
.219
HARDWARE PREPARATION AND INSTALLATION
Bus Wire
MF=
MF=
X100
X101
(X8)
(X9)
28
32
NA
14
16
18
7
8
9
4
4.5
2
2.25
1
1.125
.5
.563
.25
.281
MF=
MF=
X110
X111
(X10)
(X11)
NA
NA
20
22
10
11
5
5.5
2.5
2.75
1.25
1.375
.625
.688
.313
.344
2-5
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