HD404459 Datasheet, PDF (41/122 Pages) Renesas Technology Corp – 4-bit HMCS400-series microcomputers

HD404459 Series
Internal Oscillator Circuit
Clock Generation Circuit
See figure 25 for a block diagram of the clock generation circuit. 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 (table
22). The system oscillator can also be operated by an external clock. Bit 1 (SSR11) of system clock select
register 1 (SSR1: $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 1 (SSR1: $029) setting does not match the oscillator frequency,
subsystems using the 32.768-kHz oscillation will malfunction.
LSON
OSC₂
OSC₁
X1
X2
System ^fOSC
oscillator
1/4, 1/8,
1/16, or
1/32
f_cyc
t_cyc
division
circuit^*1
Timing
generator
circuit
ø_CPU
System
clock
selection
circuit _øPER
f_X
f_SUB
Sub-
Timing
system
1/8 or 1/4 ^tsubcyc _generator
oscillator
division
circuit
circuit^*2
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
circuit
Time-base
interrupt
Notes: 1. 1/4, 1/8, 1/16, or 1/32 division ratio can be selected by setting bits 0 and 1 of system clock
select register 2 (SSR2).
2. 1/8 or 1/4 division ratio can be selected by setting bit 2 of system clock select register 1
(SSR1).
Figure 25 Clock Generation Circuit
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