5.3
Standby Mode
5.3.1
Transition to Standby Mode
The system goes from active mode to standby mode when a SLEEP instruction is executed while
the SSBY bit in SYSCR1 is set to 1, the LSON bit in SYSCR1 is cleared to 0, and bit TMA3 in
TMA is cleared to 0. In standby mode the clock pulse generator stops, so the CPU and on-chip
peripheral modules stop functioning, but as long as the rated voltage is supplied, the contents of
CPU registers, on-chip RAM, and some on-chip peripheral module registers are retained. On-chip
RAM contents will be further retained down to a minimum RAM data retention voltage. The I/O
ports go to the high-impedance state.
5.3.2
Clearing Standby Mode
Standby mode is cleared by an interrupt (IRQ1 or IRQ0), WKP7 to WKP0 or by input at the RES
pin.
•
Clearing by interrupt
When an interrupt is requested, the system clock pulse generator starts. After the time set in bits
STS2 to STS0 in SYSCR1 has elapsed, a stable system clock signal is supplied to the entire chip,
standby mode is cleared, and interrupt exception handling starts. Operation resumes in active
(high-speed) mode if MSON = 0 in SYSCR2, or active (medium-speed) mode if MSON = 1.
Standby mode is not cleared if the I bit of CCR is set to 1 or the particular interrupt is disabled in
the interrupt enable register.
•
Clearing by RES input
When the RES pin goes low, the system clock pulse generator starts. After the pulse generator
output has stabilized, if the RES pin is driven high, the CPU starts reset exception handling. Since
system clock signals are supplied to the entire chip as soon as the system clock pulse generator
starts functioning, the RES pin should be kept at the low level until the pulse generator output
stabilizes.
5.3.3
Bits STS2 to STS0 in SYSCR1 should be set as follows.
When a crystal oscillator is used
Oscillator Settling Time after Standby Mode is Cleared
•
The table below gives settings for various operating frequencies. Set bits STS2 to STS0 for a
waiting time at least as long as the oscillation settling time.
106
ETC [ ETC ]
