7480 Group and 7481 Group User's Manual
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1.19 Power Saving Function
HARDWARE
(2)
Transition to Wait Mode
The transition from the normal mode to the wait mode is described below.
Recovery from Wait Mode by Reset Input
Execute the WIT instruction while the WIT instruction is valid.
Recovery from Wait Mode by Accepting Interrupt Request
Execute the WIT instruction while the WIT instruction is valid after the interrupt for terminating the
wait mode is set.
For the setting of the valid/invalid of the WIT instruction, refer to Section 1.19.4 Setting of Valid/
Invalid of STP and WIT Instructions.
1.19.4 Setting of Valid/Invalid of STP and WIT Instructions
In the 7480 Group and 7481 Group, the valid/invalid of the STP and WIT instructions can be selected with
the STP instruction operation control register. The STP and the WIT instruction are invalid after the system
is released from reset to prevent the program from a runaway.
Writing twice successively to the STP instruction operation control register makes the STP and the WIT
instruction valid, while non-successive writing to the register (for example, a single write) makes these
instructions invalid. As the STP and the WIT instruction remain invalid after the system is released from
reset, successive writing is used to prevent the clock oscillation from stopping due to erroneous data
written during a program runaway.
Figure 1.19.7 shows the setting of valid/invalid of the STP and WIT instructions.
Figure 1.19.7 Setting of Valid/Invalid of STP and WIT Instructions
Procedure 1 Setting interrupt disable flag of processor status register to ‘1’ (interrupt disabled)
STP and WIT instructions invalid
Procedure 2 Setting STP instruction operation control register (twice successive writing) (Note 1)
STP instruction operation control register (STPCON) [Address 00DE16]
b7
b0
1. A write of ‘1’
1
STP and WIT valid/Invalid selection
0: Valid
1: Invalid
STP instruction operation control register (STPCON) [Address 00DE16]
b7
b0
2. Selection of valid/invalid of STP and WIT instructions (Note 2)
Notes 1: A single write to the STP instruction operation control register makes the STP
and WIT instructions invalid.
2: If invalidating the STP and WIT instructions, the second write can be omitted.
Procedure 3 Clearing interrupt disable flag of processor status register to ‘0’ (interrupt enabled)
when using interrupts.