System Integration Module (SIM60)
6-42
MC68360 USER’S MANUAL
MOTOROLA
tial general system clock of 13.14 MHz. The user would then write the MF bits to raise this
frequency to the desired frequency.
NOTE
SWT clocking does not stop when the PLL is in the process of
acquiring a lock. Therefore, the user should service the SWT (re-
set its count) before and after changing the MF bits.
6.9.3.11 CLOCK DIVIDER CONTROL REGISTER (CDVCR).
The CDVCR controls the
operation of the low-power divider for the various clocks on the QUICC. It can be read or
written only in supervisor mode. Writing this register is allowed only if the CDVWP bit is zero.
The reset state of CDVCR produces the maximum frequency for all the clocks that it affects.
CDVWP—CDVCR Write Protect
This bit protects accidental writing of the CDVCR. After reset, this bit defaults to zero to
enable writing. Setting this bit prevents further writing (excluding the first write that sets
this bit).
DFSY—Division Factor for the SyncCLK
These bits define the SyncCLK frequency. Changing the value of the these bits will not
result in a loss-of-lock condition. These bits are cleared by a hardware reset. The default
value is divide by 1 (VCO/2) which is 25 MHz in a 25-MHz system.
00 = Divide by 1 (normal operation)
01 = Divide by 4
10 = Divide by 16
11 = Divide by 64
DFTM—Division Factor for the BRGCLK
These bits define the BRGCLK frequency. Changing the value of the these bits will not
result in a loss-of-lock condition. These bits are cleared by a hardware reset. The default
value is divide by 1 (VCO/2) which is 25 MHz in a 25-MHz system.
00 = Divide by 1 (normal operation)
01 = Divide by 4
10 = Divide by 16
11 = Divide by 64
INTEN—Interrupt Enable
These bits specify if the general system clock returns to high frequency (defined by the
DFNH bits) whilethe CPU32+ either has a pending interrupt or an interrupt routine in pro-
cess, either of which has a level higher than INTEN2–INTEN0. To prevent interrupts from
causing the general system clock to automatically switch to high frequency, write INTEN
with 111.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
CDVWP
0
DFSY
DFTM
INTEN
0
RRQEN
0
DFNL
0
DFNH
0
CSRC
0
0
0
0
0
0
0
0
0
0
0