Epson S1C88650 - Manual (Page 51)

S1C88650 TECHNICAL MANUAL EPSON 43
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Oscillation Circuits)
5.4.6 Control of oscillation circuit
Table 5.4.6.1 shows the control bits for the oscillation circuits.
Table 5.4.6.1 Oscillation circuit control bits
Address Bit Name SR R/W Function Comment 1 0
00FF02 D7
D6
D5
D4
D3
D2
D1
D0
EBR
WT2
WT1
WT0
CLKCHG
SOSC3
–
–
0
0
0
0
1
1
0
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
BREQ
BACK
OSC3
On
1
1
WT2
1
1
1
1
0
0
0
0
WT1
1
1
0
0
1
1
0
0
WT0
1
0
1
0
1
0
1
0
Number
of state
14
12
10
8
6
4
2
Input port
Output port
OSC1
Off
0
0
Bus release enable register
(K03 and R33 terminal specification)
Wait control register
CPU operating clock switch
OSC3 oscillation On/Off control
R/W register
R/W register
No wait
Reserved register
K03
R33
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:
Valid
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:
Valid
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).
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 OSC1
• OSC3 oscillation circuit OFF
(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
→
OSC3) after allowing
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".)