S1C63358 TECHNICAL MANUAL
EPSON
33
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)
4.4.5 Clock frequency and instruction execution time
Table 4.4.5.1 shows the instruction execution time according to each frequency of the system clock.
Table 4.4.5.1 Clock frequency and instruction execution time
Clock frequency
OSC1: 32.768 kHz
OSC1: 60 kHz
OSC3: 4 MHz
Instruction execution time (
µ
sec)
1-cycle instruction
2-cycle instruction
3-cycle instruction
61
122
183
33
66
100
0.5
1
1.5
4.4.6 I/O memory of oscillation circuit
Table 4.4.6.1 shows the I/O address and the control bits for the oscillation circuit.
Table 4.4.6.1 Control bits of oscillation circuit
Address
Comment
D3
D2
Register
D1
D0
Name
Init
∗
1
1
0
FF00H
CLKCHG OSCC
0
VDC
R
R/W
R/W
CLKCHG
OSCC
0
∗
3
VDC
0
0
–
∗
2
0
OSC3
On
2.25 V
OSC1
Off
1.35 V
CPU clock switch
OSC3 oscillation On/Off
Unused
CPU operating voltage switch (1.35 V: OSC1, 2.25 V: OSC3)
*1 Initial value at initial reset
*2 Not set in the circuit
*3 Constantly "0" when being read
VDC: CPU operating voltage switching register (FF00H•D0)
It is used to switch the operating voltage V
D1
, when the crystal oscillation circuit has been selected as the
OSC1 oscillation circuit by mask option.
When "1" is written: 2.25 V (for OSC3 operation)
When "0" is written: 1.35 V (for OSC1 operation)
Reading: Valid
When switching the CPU system clock, the operating voltage V
D1
should also be switched according to
the clock.
When switching from OSC1 to OSC3, first set V
D1
to 2.25 V. After that maintain 2.5 msec or more, and
then turn the OSC3 oscillation ON.
When switching from OSC3 to OSC1, set V
D1
to 1.35 V after switching to OSC1 and turning the OSC3
oscillation OFF.
When the CR oscillation circuit has been selected as the OSC1 oscillation circuit by mask option, setting
of this register does not affect the operating voltage V
D1
, and the V
D1
voltage is fixed at 2.25 V.
At initial reset, this register is set to "0".
OSCC: OSC3 oscillation control register (FF00H•D2)
Controls oscillation ON/OFF for the OSC3 oscillation circuit.
When "1" is written: OSC3 oscillation ON
When "0" is written: OSC3 oscillation OFF
Reading: Valid
When it is necessary to operate the CPU at high speed, set OSCC to "1". At other times, set it to "0" to
reduce current consumption. Furthermore, when the crystal oscillation circuit has been selected as the
OSC1 oscillation circuit by mask option, it is necessary to switch the operating voltage V
D1
when turning
the OSC3 oscillation circuit ON and OFF
At initial reset, this register is set to "0".
