S1C88348/317/316/308 TECHNICAL SOFTWARE
EPSON
II-11
4 OSCILLATION CIRCUIT
4 OSCILLATION CIRCUIT
I/O Map
Specifications
CPU clock switching
(1) osc1toosc3: Switching from OSC1 to OSC3
Checks supply voltage and switches system clock from OSC1 (low power mode, VD1 = 1.3 V) to
OSC3 (normal mode, VD1 = 2.2 V).
(2) osc3toosc1: Switching from OSC3 to OSC1
Switches system clock from OSC3 (normal mode, VD1 = 2.2 V) to OSC1 (low power mode, VD1 = 1.3 V).
Notes
(1) Delay routines for the OSC3 oscillation stabilization waiting time, VD1 voltage stabilization waiting
time (wait time until OSC3 turns on after operating mode switching, 5 msec or more), etc. are not
included in this program example, so it is necessary to create them separately using a hardware timer
or software timer. (external call: osc3_delay, vd1_delay)
(2) Switching operating modes when the supply voltage is lower than the VD1 setting may cause a
malfunction. Hence, perform operating mode switching only after making sure that the power
voltage of SVD is more than the VD1 setting voltage (absolute value). (external call: svd_auto)
The program example sets the NG flag (vdd_ngf) and terminates processing without switching the
system clock, when the supply voltage is lower than the VD1 setting.
(3) When switching from OSC3 to OSC1 (VD1 = 2.2 V
→ 1.3 V), the program example does not perform
special checking of the supply voltage of SVD if the supply voltage is already more than the VD1
setting.
(4) Pay special attention the delay routine setting since the OSC3 oscillation stabilization waiting time
varies somewhat depending on the oscillator and externally attached parts used.
(5) Because of operating voltage considerations, both modes (low power mode and high speed mode)
cannot be used in one application.
Address Bit
Name
SR R/W
Function
Comment
10
00FF02
D7
D6
D5
D4
D3
D2
D1
D0
EBR
WT2
WT1
WT0
CLKCHG
OSCC
VDC1
VDC0
Bus release enable register
(K11 and R51 terminal specification)
Wait control register
CPU operating clock switch
OSC3 oscillation On/Off control
Operating mode selection
*1
*1 This is just R/W register on S1C88308.
0
R/W
BREQ
BACK
OSC3
On
WT2
1
0
WT1
1
0
1
0
Number
of state
14
12
10
8
6
4
2
No wait
Input port
Output port
OSC1
Off
K11
R51
VDC1
1
0
VDC0
×
1
0
High speed (VD1=3.3V)
Low power (VD1=1.3V)
Normal
(VD1=2.2V)
WT0
1
0
1
0
1
0
1
0
Operating mode