HD404449 Datasheet, PDF (39/123 Pages) Hitachi Semiconductor – HD404449 SERIES

HD404449 Series
Internal Oscillator Circuit
A block diagram of the clock generation circuit is shown in figure 25. As shown in table 22, a ceramic
oscillator or crystal oscillator can be connected to OSC₁ and OSC₂, and a 32.768-kHz oscillator can be
connected to X1 and X2. The system oscillator can also be operated by an external clock. Bit 1 (SSR1) of
the system clock select register (SSR: $029) must be selected according to the frequency of the oscillator
connected to OSC₁ and OSC₂ (figure 26).
Note: If the system clock select register (SSR: $029) setting does not match the oscillator frequency,
subsystems using the 32.768-kHz oscillation will malfunction.
LSON
OSC₂
OSC₁
X1
X2
System ^fOSC 1/4 ^fcyc Timing
oscillator
division
circuit
t_cyc
generator
circuit
f_X
f_SUB
Sub-
system
1/8 or 1/4
Timing
division ^tsubcyc generator
oscillator
circuit^Note
circuit
ø_CPU
System
clock
selection
ø_PER
TMA3
CPU with ROM,
RAM, registers,
flags, and I/O
Peripheral
function
interrupt
1/8
division
circuit
Timing
f_W generator
circuit
t_Wcyc
Time-base
clock øCLK
selection
Time-base
interrupt
Note: 1/8 or 1/4 division ratio can be selected by setting bit 2 of the system
clock select register (SSR: $029).
Figure 25 Clock Generation Circuit
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