Control Of Oscillation Circuit; Programming Notes - Epson S1C88650 Technical Manual

5.4.6 Control of oscillation circuit

Table 5.4.6.1 shows the control bits for the oscillation circuits.
Address Bit Name
00FF02 D7 EBR
D6 WT2
D5 WT1
D4 WT0
D3 CLKCHG
D2 SOSC3
D1 –
D0 –
SOSC3: 00FF02H•D2
Controls the ON and OFF settings of the OSC3
oscillation circuit.
When "1" is written: OSC3 oscillation ON
When "0" is written: OSC3 oscillation OFF
Reading:
When the CPU and some peripheral circuits are to
be operated at high speed, SOSC3 is to be set to "1".
At all other times, it should be set to "0" in order to
reduce current consumption.
At initial reset, SOSC3 is set to "1" (OSC3 oscillation
ON).
CLKCHG: 00FF02H•D3
Selects the operating clock for the CPU.
When "1" is written: OSC3 clock
When "0" is written: OSC1 clock
Reading:
When the operating clock for the CPU is switched
to OSC3, CLKCHG should be set to "1" and when
the clock is switched to OSC1, CLKCHG should be
set to "0".
At initial reset, CLKCHG is set to "1" (OSC3 clock).
S1C88650 TECHNICAL MANUAL
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Oscillation Circuits)
Table 5.4.6.1 Oscillation circuit control bits
Function
Bus release enable register
(K03 and R33 terminal specification)
Wait control register
WT2 WT1 WT0
1 1 1
1 1 0
1 0 1
1 0 0
0 1 1
0 1 0
0 0 1
0 0 0
CPU operating clock switch
OSC3 oscillation On/Off control
R/W register
R/W register
Valid
Valid
1
K03
BREQ Input port
R33
BACK Output port
Number
of state
14
12
10
8
6
4
2
No wait
OSC3
On
1
1

5.4.7 Programming notes

(1) When the high speed CPU operation is not
necessary, you should operate the peripheral
circuits according to the setting outline indicate
below.
• CPU operating clock
• OSC3 oscillation circuit
(When the OSC3 clock is not necessary for
some peripheral circuits.)
(2) Since several msec to several tens of msec are
necessary for the oscillation to stabilize after
turning the OSC3 oscillation circuit ON.
Consequently, you should switch the CPU
operating clock (OSC1
for a sufficient waiting time once the OSC3
oscillation goes ON. (The oscillation start time
will vary somewhat depending on the oscillator
and on the externally attached parts. Refer to the
oscillation start time example indicated in
Chapter 8, "ELECTRICAL CHARACTERIS-
TICS".)
(3) When switching the clock from OSC3 to OSC1, be
sure to switch OSC3 oscillation OFF with
separate instructions. Using a single instruction
to process simultaneously can cause a malfunc-
tion of the CPU.
(4) When switching the system clock from OSC3 to
OSC1 immediately after the power is turned on,
it is necessary to wait the OSC1 oscillation to
stabilize before the clock can be switched. The
OSC3 oscillation takes several tens of msec to
several seconds until it has completely stabilized.
(The oscillation start time will vary somewhat
depending on the oscillator and on the externally
attached parts. Refer to the oscillation start time
example indicated in Chapter 8, "ELECTRICAL
CHARACTERISTICS".)
EPSON
0 SR R/W Comment
0 R/W
0 R/W
0 R/W
0 R/W
1 R/W
OSC1
1 R/W
Off
0 R/W
0 Reserved register
0 R/W
0
OSC1
OFF
OSC3) after allowing
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