S1C88348/317/316/308 TECHNICAL HARDWARE
EPSON
I-53
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Oscillation Circuits and Operating Mode)
When you must operate on OSC3, you can change
to high speed operation by turning the OSC3
oscillation circuit ON and switching over the
system clock. In this case, since several msec to
several tens of msec are necessary for the oscillation
to stabilize after turning the OSC3 oscillation circuit
ON, you should switch over the clock after
stabilization time has elapsed. (The oscillation start
time will vary somewhat depending on the oscilla-
tor and on the externally attached parts. Refer to
the oscillation start time example indicated in
Chapter 7, "ELECTRICAL CHARACTERISTICS".)
When switching over from the OSC3 to the OSC1,
turn the OSC3 oscillation circuit OFF immediately
following the clock changeover. The basic clock
switching procedure is as described above, how-
ever, you must also combine it with the changeover
of the operating mode to permit low current
consumption and high speed operation.
Figure 5.4.6.1 indicates the status transition dia-
gram for the operation mode and clock changeover.
Note: When turning ON the OSC3 oscillation circuit
after switching the operating mode, you should
allow a minimum waiting time of 5 msec.
Note: Do not turn the OSC3 oscillation circuit ON
in the low power mode.
Do not switch over the operating mode
(normal mode
high speed mode) in the
OSC3 oscillation circuit ON status, as this
will cause faulty operation.
You can not use two modes, the low power
mode and the high speed mode on one
application, with respect to the operating
voltages.
When CR oscillation is selected for the
OSC1 oscillation circuit, the operating mode
is fixed in the normal mode to stabilize the
oscillation frequency. Consequently, settings
of the mode setting registers VDC0 and
VDC1 become invalid.
5.4.6 Switching the CPU clocks
You can use either OSC1 or OSC3 as the system
clock for the CPU and you can switch over by
means of software.
You can save power by turning the OSC3 oscilla-
tion circuit off while the CPU is operating in OSC1.
*
The return destination from the standby status becomes the program execution status
prior to shifting to the standby status
Fig. 5.4.6.1
Status transition diagram
for the operation mode
and clock changeover
ON
ON or OFF
STOP
HALT status
OSC1
OSC3
CPU clock
OFF
STOP
SLEEP status
OSC1
OSC3
CPU clock
Program Execution Status
Standby Status
HALT instruction
SLP instruction
*
Interrupt
*
Interrupt
(Input interrupt)
VDC0=0
VDC1=0
OSCC=0
RESET
OSCC=1
CLKCHG=0
CLKCHG=1
OSCC=0
OSCC=1
CLKCHG=0
CLKCHG=1
ON
OFF
OSC1
ON
OFF
OSC1
ON
OSC1
ON
OSC1
ON
OSC3
ON
OSC3
High speed mode
ON
OFF
OSC1
Normal mode
Low power mode
High speed mode
Normal mode
High speed mode
Normal mode
VDC0=
VDC1=1
VDC0=1
VDC1=0
VDC0=0
VDC1=0
×
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock
OSC1
OSC3
CPU clock