
CHAPTER 5 CLOCK GENERATOR
User’s Manual U16315EJ3V1UD
107
The fastest instruction can be executed in 2 clocks of the CPU clock in the 78K0/KD1. Therefore, the relationship
between the CPU clock (fCPU) and the minimum instruction execution time is as shown in Table 5-2.
Table 5-2. Relationship Between CPU Clock and Minimum Instruction Execution Time
Minimum Instruction Execution Time: 2/fCPU
X1 Input Clock
Note 1
CPU Clock (fCPU)
At 10 MHz
Operation
At 12 MHz
Operation
Note 2
Internal Oscillation Clock
Note 1
(at 240 kHz (TYP.) Operation)
Subsystem Clock
(at 32.768 kHz Operation)
fX
0.2
s
0.166
s
8.3
s (TYP.)
fX/2
0.4
s
0.333
s
16.6
s (TYP.)Note 3
fX/2
2
0.8
s
0.666
s
Setting prohibited
fX/2
3
1.6
s
1.333
s
Setting prohibited
fX/2
4
3.2
s
2.666
s
Setting prohibited
fXT/2
122.1
s
Notes 1.
The main clock mode register (MCM) is used to set the CPU clock (X1 input clock/internal oscillation
clock) (see Figure 5-4).
2.
Expanded-specification products of standard products and (A) grade products only
3.
Setting is prohibited for the (A1) and (A2) grade products.
(2) Internal oscillation mode register (RCM)
This register sets the operation mode of the internal oscillator.
This register is valid when “Can be stopped by software” is set for the internal oscillator by a mask option, and the
X1 input clock or subsystem clock is selected as the CPU clock. If “Cannot be stopped” is selected for the
internal oscillator by a mask option, settings for this register are invalid.
RCM can be set by a 1-bit or 8-bit memory manipulation instruction.
RESET input clears this register to 00H.
Figure 5-3. Format of Internal Oscillation Mode Register (RCM)
Address: FFA0H
After reset: 00H
R/W
Symbol
7
6
5
4
3
2
1
<0>
RCM
0
RSTOP
Internal oscillator oscillating/stopped
0
Internal oscillator oscillating
1
Internal oscillator stopped
Caution
Make sure that bit 1 (MCS) of the main clock mode register (MCM) is 1 before setting
RSTOP.