HD404639R Datasheet, PDF (38/135 Pages) Renesas Technology Corp – 4-Bit Single-Chip Microcomputer

HD404639R Series
Internal Oscillator Circuit
A block diagram of the clock generation circuit is shown in figure 23. As shown in table 20, 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. System clock
select register 1 (SSR1: $029) and system clock select register 2 (SSR2: $02A) must be selected according
to the frequency of the oscillator connected to OSC₁ and OSC₂ (figure 24).
Note: If the SSR10, SSR11, SSR22 and SSR23 setting does not match the oscillator frequency, the
DTMF generator and subsystems using the 32.768-kHz oscillation will malfunction.
OSC₂
OSC₁
X1
X2
System ^fOSC
1/4 or
1/8 or
f_cyc
oscillator
1/16 or
1/32
t_cyc
division
circuit* ¹
Timing
generator
circuit
f_X
f_SUB
Sub-
system
1/8 or 1/4
Timing
division ^tsubcyc generator
oscillator
circuit*²
circuit
LSON
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
Notes: 1. 1/4, 1/8, 1/16 or 1/32 division ratio can be selected by setting bits 1 and 0 of
system clock select register 2 (SSR2: $02A).
2. 1/8 or 1/4 division ratio can be selected by setting bit 2 of system clock select
register 1 (SSR1: $029).
Figure 23 Clock Generation Circuit
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