Prescalers - Renesas F-ZTAT H8 Series Hardware Manual

4.4

Prescalers

The H8/3857 Group and H8/3854 Group are equipped with two on-chip prescalers having
different input clocks (prescaler S and prescaler W). Prescaler S is a 13-bit counter using the
system clock (φ) as its input clock. Its prescaled outputs provide internal clock signals for on-chip
peripheral modules. Prescaler W is a 5-bit counter using a 32.768-kHz signal divided by 4 (φ
as its input clock. Its prescaled outputs are used by timer A as a time base for timekeeping.
Prescaler S (PSS): Prescaler S is a 13-bit counter using the system clock (φ) as its input clock. It
is incremented once per clock period.
Prescaler S is initialized to H'0000 by a reset, and starts counting on exit from the reset state.
In standby mode, watch mode, subactive mode, and subsleep mode, the system clock pulse
generator stops. Prescaler S also stops and is initialized to H'0000.
The CPU cannot read or write prescaler S.
The output from prescaler S is shared by timer A, timer B, timer C*, timer F, SCI1*, SCI3, the
A/D converter, LCD controller, and 14-bit PWM*. The divider ratio can be set separately for each
on-chip peripheral function.
In active (medium-speed) mode the clock input to prescaler S is φ
Note: * This is a function of the H8/3857 Group only, and is not provided in the H8/3854
Group.
Prescaler W (PSW): Prescaler W is a 5-bit counter using a 32.768 kHz signal divided by 4 (φ
as its input clock.
Prescaler W is initialized to H'00 by a reset, and starts counting on exit from the reset state.
Even in standby mode, watch mode, subactive mode, or subsleep mode, prescaler W continues
functioning so long as clock signals are supplied to pins X
Prescaler W can be reset by setting 1s in bits TMA3 and TMA2 of timer mode register A (TMA).
Output from prescaler W can be used to drive timer A, in which case timer A functions as a time
base for timekeeping.
4. Clock Pulse Generators
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