HD404369 Datasheet, PDF (55/117 Pages) Hitachi Semiconductor – 4-bit HMCS400-Series microcomputer

HD404369 Series
Prescalers
The MCU has the following two prescalers, S and W.
The prescaler operating conditions are listed in table 24, and the prescaler output supply is shown in figure
35. The timer A–C 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.
Prescaler Operation
Prescaler S: 11-bit counter that inputs the 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 subactive modes and
at MCU reset.
Prescaler W: Five-bit counter that inputs the X1 input clock signal (32-kHz crystal oscillation) divided by
eight. After being reset to $00 by MCU reset, prescaler W divides the input clock. Prescaler W can be reset
by software.
Table 24 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
Subsystem
f_X/8
clock
f_X/4 or f_X/8
System
clock
Clock
selector
Prescaler W
Prescaler S
Figure 35 Prescaler Output Supply
Timer A
Timer B
Timer C
Serial
Alarm output
circuit
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