HD404654 Datasheet, PDF (33/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
Internal Oscillator Circuit
A block diagram of the clock generation circuit is shown in figure 17. As shown in table 18, a ceramic
oscillator or crystal oscillator can be connected to OSC₁ and OSC₂. The system oscillator can also be
operated by an external clock. Bit 1 (SSR11) of system clock select register 1 (SSR1: $029) and bit 2
(SSR22) of system clock select register 2 (SSR2: $02A) must be selected according to the frequency of the
oscillator connected to OSC₁ and OSC₂ (figure 18).
Note: If the SSR10, SSR11 and SSR22 setting does not match the oscillator frequency, the DTMF
generator will malfunction.
After RESET input or after stop mode has been cancelled, the division ratio of the system clock can be
selected as 1/4 or 1/32 by setting the SEL pin level.
• 1/4 division ratio: Connect SEL to V_CC.
• 1/32 division ratio: Connect SEL to GND.
OSC₂
OSC₁
System ^{fOSC 1/4 or fcyc} Timing
oscillator
1/32
division
t_cyc
generator
circuit
circuit*
φ_CPU
φ_PER
Note: * 1/4 or 1/32 division ratio can be selected by pin SEL.
Figure 17 Clock Generation Circuit
CPU with ROM,
RAM, registers,
flags, and I/O
Peripheral
function
interrupt
31