HD404669 Datasheet, PDF (56/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 Series
Prescalers
The MCU has the following two prescalers, S and W.
The prescalers operating conditions are listed in table 17, and the prescalers output supply is shown in
figure 38. The timers A, C, D input clocks except external events, the serial transmit clock except the
external clock, are selected from the prescaler outputs, depending on corresponding mode registers.
Table 17 Prescaler Operating Conditions
Prescaler
Input Clock
Reset Conditions
Stop Conditions
Prescaler S
System clock (in active and
standby mode),
Subsystem clock (in subactive
mode)
MCU reset
MCU reset,
stop mode,
watch mode
Prescaler W
Clock derived by dividing
subsystem clock 32.768 kHz
oscillation by 8
MCU reset,
software*
MCU reset,
stop mode
Note: * If bits TMA3 to TMA1 in timer mode register A (TMA) are all set to 1, PSW is cleared to $00.
Subsystem
clock
Prescaler W
System
clock
Clock
selector
Prescaler S
Timer A
Timer C
Timer D
Serial
interface 1
Figure 38 Prescaler Output Supply
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 stop 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.
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