HD404849 Datasheet, PDF (55/125 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404849 Series
Prescalers
The MCU has two prescalers, S and W.
The prescaler operating conditions are listed in table 25, and the prescalers output supply is shown in figure
39. The timer A–D input clocks except external events, the serial transmit clock except the external clock,
and the LCD controller/driver operating 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 divided X1 input clock signal (32-kHz crystal oscillation).
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 Input Clock
Prescaler S
System clock (in active and standby
mode), subsystem clock (in subactive
mode)
Prescaler W 32-kHz crystal oscillation
Reset Conditions
MCU reset
Stop Conditions
MCU reset, stop mode,
watch mode
MCU reset, software MCU reset, stop mode
Subsystem ^fX^/8
clock
f_X/4 or f_X/8
System
clock
Clock
selector
Prescaler W
Prescaler S
Figure 39 Prescaler Output Supply
LCD
Timer A
Timer B
Timer C
Timer D
Serial
interface
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