
26
EPSON
S1C63567 TECHNICAL MANUAL
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)
4.3.4 Switching the CPU operating clock
The CPU system clock is switched to OSC1 or OSC3 by the software (CLKCHG register).
When OSC3 is to be used as the CPU system clock, first turn the OSC3 oscillation ON and switch the
clock after waiting 5 msec or more for oscillation stabilization.
When switching from OSC3 to OSC1, turn the OSC3 oscillation circuit OFF after switching the clock.
OSC1
→ OSC3
OSC3
→ OSC1
1. Set OSCC to "1" (OSC3 oscillation ON).
1. Set CLKCHG to "0" (OSC3
→ OSC1).
2. Maintain 5 msec or more.
2. Set OSCC to "0" (OSC3 oscillation OFF).
3. Set CLKCHG to "1" (OSC1
→ OSC3).
Note: When switching the clock form OSC3 to OSC1, use a separate instruction for switching the OSC3
oscillation OFF. An error in the CPU operation can result if this processing is performed at the
same time by the one instruction.
4.3.5 Clock frequency and instruction execution time
Table 4.3.5.1 shows the instruction execution time according to each frequency of the system clock.
Table 4.3.5.1 Clock frequency and instruction execution time
Clock frequency
OSC1: 32.768 kHz
OSC1: 60 kHz
OSC3: 3.58 MHz
Instruction execution time (
sec)
1-cycle instruction
2-cycle instruction
3-cycle instruction
61
122
183
33
67
100
0.56
1.12
1.68
4.3.6 I/O memory of oscillation circuit
Table 4.3.6.1 shows the I/O address and the control bits for the oscillation circuit.
Table 4.3.6.1 Control bits of oscillation circuit
Address
Comment
D3
D2
Register
D1
D0
Name
Init 1
10
FF00H
CLKCHG OSCC
0
Dummy
R
R/W
CLKCHG
OSCC
0 3
Dummy
0
– 2
0
OSC3
On
OSC1
Off
CPU clock switch
OSC3 oscillation On/Off
Unused
General-purpose register
*1 Initial value at initial reset
*2 Not set in the circuit
*3 Constantly "0" when being read
OSCC: OSC3 oscillation control register (FF00HD2)
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.
At initial reset, this register is set to "0".