Datasheet

78K0/Kx2-L CHAPTER 5 CLOCK GENERATOR
R01UH0028EJ0400 Rev.4.00 237
Sep 27, 2010
5.6.8 Time required for switchover of CPU clock and main system clock
By setting bits 0 to 2 (PCC0 to PCC2) and bit 4 (CSS) of the processor clock control register (PCC), the CPU clock can
be switched (between the main system clock and the subsystem clock) and the division ratio of the main system clock can
be changed.
The actual switchover operation is not performed immediately after rewriting to PCC; operation continues on the pre-
switchover clock for several clocks (refer to Tables 5-8 and 5-9).
Whether the CPU is operating on the main system clock or the subsystem clock
Note
can be ascertained using bit 5 (CLS)
of the PCC register.
Note 78K0/KC2-L only
Table 5-8. Time Required for Switchover of CPU Clock and Main System Clock Cycle Division Factor (78K0/KY2-L,
78K0/KA2-L, and 78K0/KB2-L)
Set Value Before
Switchover
Set Value After Switchover
PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0 PCC2 PCC1 PCC0
0 0 0 0 0 1 0 1 0 0 1 1 1 0 0
0 0 0 16 clocks 16 clocks 16 clocks 16 clocks
0 0 1 8 clocks 8 clocks 8 clocks 8 clocks
0 1 0 4 clocks 4 clocks 4 clocks 4 clocks
0 1 1 2 clocks 2 clocks 2 clocks 2 clocks
1 0 0 1 clock 1 clock 1 clock 1 clock
Remark The number of clocks listed in Table 5-8 is the number of CPU clocks before switchover.
Table 5-9. Time Required for Switchover of CPU Clock and Main System Clock Cycle Division Factor
(78K0/KC2-L)
Set Value Before
Switchover
Set Value After Switchover
CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0 CSS PCC2 PCC1 PCC0CSS PCC2 PCC1 PCC0
0 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 1
× × ×
0 0 0 16 clocks 16 clocks 16 clocks 16 clocks fXP/fSUB clocks
0 0 1 8 clocks 8 clocks 8 clocks 8 clocks fXP/2fSUB clocks
0 1 0 4 clocks 4 clocks 4 clocks 4 clocks fXP/4fSUB clocks
0 1 1 2 clocks 2 clocks 2 clocks 2 clocks fXP/8fSUB clocks
0
1 0 0 1 clock 1 clock 1 clock 1 clock f
XP/16fSUB clocks
1
× × ×
2 clocks 2 clocks 2 clocks 2 clocks 2 clocks
Caution Selection of the main system clock cycle division factor (PCC0 to PCC2) and switchover from the
main system clock to the subsystem clock (changing CSS from 0 to 1) should not be set
simultaneously.
Simultaneous setting is possible, however, for selection of the main system clock cycle division
factor (PCC0 to PCC2) and switchover from the subsystem clock to the main system clock (changing
CSS from 1 to 0).
Remark 1. The number of clocks listed in Table 5-9 is the number of CPU clocks before switchover.