HD404459 Datasheet, PDF (58/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
Prescalers
The MCU has two prescalers, S and W. See table 25 and figure 40.
Both the timers A–D input clocks except external events and the serial transmit clock except the external
clock are selected from the prescaler outputs, depending on corresponding mode registers.
32-kHz
f_X/8
crystal
oscillator
f_X/4 or f_X/8
Prescaler W
System
clock
Clock
selector
Prescaler S
Timer A
Timer B
Timer C
Timer D
Serial
Figure 40 Prescaler Output Supply
Prescaler Operation
Prescaler S: 11-bit counter that inputs a system clock signal. After being reset to $000 by MCU reset,
prescaler S divides the system clock. Prescaler S keeps counting, except in watch and stop modes and at
MCU reset.
Prescaler W: Five-bit counter that inputs the X1 input clock signal (32-kHz crystal oscillation) divided.
After being reset to $00 by MCU reset, prescaler W divides the input clock. Prescaler W can be reset by
software.
Table 25 Prescaler Operating Conditions
Prescaler
Prescaler S
Prescaler W
Input Clock
Reset Conditions
System clock
(in active and standby
mode),
Subsystem clock
(in subactive mode)
MCU reset
32-kHz crystal oscillation MCU reset, software
Stop Conditions
MCU reset,
stop mode,
watch mode
MCU reset,
stop mode
56