HD404374 Datasheet, PDF (54/161 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip A/D Converter

HD404374/HD404384/HD404389/HD404082/HD404084 Series
Internal Oscillator Circuit
Figure 20 shows the clock pulse generator circuit. As shown in table 21, a ceramic oscillator or crystal
oscillator can be connected to OSC1 and OSC2, and a 32.768 kHz crystal oscillator can be connected to X1
and X2. External clock operation is possible for the system oscillator. CR oscillation for system oscillator
is possible. CR oscillation function is optional. Set bit 1 (SSR1) of the system clock select register (SSR:
$004) according to the frequency of the oscillator connected to OSC1 and OSC2 (figure 22).
Note: If the setting of bit 1 in the system clock select register does not match the frequency of the system
oscillator, the subsystem using 32.768 kHz oscillation will not operate correctly in the HD404374
Series.
Also, the CR oscillation frequency differs depending on the operating voltage and resistance value. Set bit 1
of the system clock select register to match the operating frequency. Note that if the frequency being used
does not match the setting of bit 1 of the system clock select register, subsystems using the 32.768 kHz
oscillation frequency will not operate correctly.
OSC2
System
oscillator
fOSC _{1/4 or 1/32} fcyc _Timing
division tcyc generation
circuit*
circuit
OSC1
X2
LSON
CPU
System
clock
selection
circuit
PER
CPU
• ROM
• RAM
• Registers, flags
• I/O
Peripheral
functions
Interrupts
Sub
system
clock
oscillator
fx _{1/8 or 1/4} fSUB _Timing
division tsubcyc generator
circuit*
circuit
X1
HD404374 series
1/8
division
circuit
fW ^Timing
twcyc ^generation
circuit
TMA3 bit
Time
base
CLK
clock
selection
circuit
Timer A
interrupts
Notes: * The division ratio can be selected by setting bit 0 or bit 2 in the system clock select register
(SSR:$004).
Figure 20 Clock Pulse Generator Circuit
Rev.5.00, Sep.11.2003, page 54 of 161