245
Chapter 9
Clock Generator
Preliminary User’s Manual U15839EE1V0UM00
9.3.4 Processor Clock Control Register (PCC)
This is an 8-bit register that controls the CPU clock. Data can be written to it only in a sequence of spe-
cific instructions so that its contents are not easily rewritten in case of program hang-up. See also
PHCMD register.
The setup of this register can be changed only one time. After a power save mode has been released,
the CPU clock is supplied by the main oscillator and again a new clock source can be selected.
This register can be read or written in 8-bit units.
Figure 9-5:
Processor Clock Control Register (PCC) (1/2)
7
6
5
4
3
2
1
0
Address
Initial
value
PCC
FRC
0
MFRC
CLS
0
0
CKS1
CKS0
FFFFF828H
00H
Bit name
Function
FRC
Sub-system clock oscillation circuit control of internal return resistance.
0: Resistance connected
1: Resistance disconnected
Remark:
The FRC bit must always remain cleared (0) while sub-system clock operation is
enabled.
MFRC
Main-system clock oscillation circuit control of internal return resistance
0: Resistance connected
1: Resistance disconnected
Remark:
The initial setting of the MFRC bit must not be changed at anytime. To secure proper
operation of the main-system clock, the internal feed-back resistance must remain
connected always.
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