Datasheet

CHAPTER 5 CLOCK GENERATORS
User’s Manual U18172EJ3V0UD
76
5.3 Registers Controlling Clock Generators
The clock generators are controlled by the following four registers.
• Processor clock control register (PCC)
• Preprocessor clock control register (PPCC)
• Low-speed internal oscillation mode register (LSRCM)
• Oscillation stabilization time select register (OSTS)
( μ PD78F920x only)
(1) Processor clock control register (PCC) and preprocessor clock control register (PPCC)
These registers are used to specify the division ratio of the system clock.
PCC and PPCC are set by using a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets PCC and PPCC to 02H.
Figure 5-2. Format of Processor Clock Control Register (PCC)
Address: FFFBH, After reset: 02H, R/W
Symbol 7 6 5 4 3 2 1 0
PCC 0 0 0 0 0 0 PCC1 0
Figure 5-3. Format of Preprocessor Clock Control Register (PPCC)
Address: FFF3H, After reset: 02H, R/W
Symbol 7 6 5 4 3 2 1 0
PPCC 0 0 0 0 0 0 PPCC1 PPCC0
PPCC1 PPCC0 PCC1 Selection of CPU clock (fCPU)
Note 1
0 0 0 fX
0 1 0 fX/2
Note 2
0 0 1 fX/2
2
1 0 0 fX/2
2 Note 3
0 1 1 fX/2
3 Note 2
1 0 1 fX/2
4 Note 3
Other than above Setting prohibited
Notes 1. The setting range of the CPU clock differs depending on the supply voltage to be used.
Be sure to refer to CPU clock and peripheral clock frequencies described in AC
Characteristics in CHAPTER 19.
2. If PPCC = 01H, the clock (f
XP) supplied to the peripheral hardware is fX/2.
3. If PPCC = 02H, the clock (f
XP) supplied to the peripheral hardware is fX/2
2
.
<R>
<R>