CHAPTER 6 CLOCK GENERATION FUNCTION
User’s Manual U13850EJ4V0UM
160
6.3 Clock Output Function
This function outputs the CPU clock via the CLKOUT pin.
When clock output is enabled, the CPU clock is output via the CLKOUT pin. When it is disabled, a low-level
signal is output via the CLKOUT pin.
Output is stopped in the IDLE or STOP mode (fixed to low level).
This function is controlled via the DCLK1 and DCLK0 bits in the PSC register.
The high-impedance status is set during the reset period. After reset is canceled, low level is output.
Caution While CLKOUT is output, changing the CPU clock (CK2 to CK0 bits of PCC register) is disabled.
6.3.1 Control registers
(1) Processor clock control register (PCC)
This is a specific register. It can be written to only when a specified combination of sequences is used (see
3.4.9
Specific registers
). This register can be read/written in 8- or 1-bit units.
Figure 6-2. Format of Processor Clock Control Register (PCC)
After reset: 03H
R/W
Address: FFFFF074H
<7>
<6>
5
4
3
<2>
1
0
PCC
FRC
MCK
0
0
0
CK2
CK1
CK0
FRC
Selection of internal feedback resistor for sub clock
0
Use
1
Do not use
MCK
Operation of main clock (main system clock)
0
Operate
1
Stop
CK2
Note
CK1
CK0
Selection of CPU clock
0
0
0
f
XX
0
0
1
f
XX
/2
0
1
0
f
XX
/4
0
1
1
f
XX
/8
1
X
X
f
XT
(sub clock)
Note
If manipulating CK2, do so in 1-bit units. In the case of 8-bit manipulation, do not change the values of
CK1 and CK0.
Содержание MPD703030A
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