6 CLOCK MANAGEMENT UNIT (CMU)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
6-15
Standby Modes
6.9
The S1C33L26 supports two standby modes: HALT and SLEEP. Power consumption on the chip can be greatly re-
duced by placing the CPU in one of these standby modes.
HALT Mode
6.9.1
The CPU suspends program execution upon executing the halt instruction and enters HALT mode. HALT mode is
effective in reducing power consumption on the chip when running the CPU is unnecessary, such as when waiting
for external input or responses from peripheral circuits.
In HALT mode, CCLK stops so the CPU, CCU, and IRAM stop operating. Furthermore, BCLK (bus-related mod-
ules) can be stopped in HALT mode (after the halt instruction is executed) by setting BCLK_EN/CMU_CLKCTL
register to 0 (see Sections 6.7.2 for BCLK). The other internal peripheral circuits remain in the state (idle or operat-
ing) held when the halt instruction was executed.
The CPU is released from HALT mode by initial reset, an NMI or other interrupt, or a forcible break from the de-
bugger. When an interrupt is used to cancel HALT mode, the C33 PE Core uses the interrupt signal sent from the
interrupt controller (ITC). Therefore, the interrupts used to cancel HALT mode must be enabled in the interrupt
source modules. The C33 PE Core can restart from HALT mode even if the PSR is set to disable interrupts.
When the IE (interrupt enable) bit in the PSR is set to 1 (enabled), the C33 PE Core executes the interrupt handler
routine after HALT mode is canceled. When the IE bit is set to 0 (disabled), an interrupt does not occur and the C33
PE Core resumes execution from the instruction that follows the halt instruction.
The #NMI signal releases the CPU from HALT mode when it goes low level.
Note: The PCLK2 clock must be enable before setting the S1C33L26 into HALT mode, as it is required
for ITC module when the C33 PE Core wakes up from HALT mode.
SLEEP Mode
6.9.2
The CPU suspends program execution upon executing the slp instruction and enters SLEEP mode. In SLEEP mode,
the CPU stops operating and the CMU stops supplying clocks. Therefore, all peripheral modules (except for the
OSC1 oscillator circuit and RTC) stop operating.
The CPU is reawaken from SLEEP mode by initial reset, an RTC interrupt, an NMI, or other interrupt from an ex-
ternal device (port input interrupt).
The C33 PE Core can restart from SLEEP mode even if the PSR is set to disable interrupts. When the IE (interrupt
enable) bit in the PSR is set to 0 (disabled), an interrupt does not occur and the C33 PE Core resumes execution
from the instruction that follows the slp instruction. When the IE bit is set to 1 (enabled), the C33 PE Core executes
the interrupt handler routine after SLEEP mode is canceled.
The #NMI signal releases the CPU from SLEEP mode when it goes low level.
Notes: • In SLEEP mode, there is a time lag between inputting an interrupt signal for wake-up and
starting the clock supply to the interrupt source module, so a delay will occur until the interrupt
flag is set. Therefore, no interrupt will occur if the interrupt signal is negated before the clock is
supplied, as the interrupt flag is not set.
Furthermore, additional time is needed for the C33 PE Core to accept the interrupt request
from the ITC, the C33 PE Core may execute a few instructions that follow the slp instruction
before it executes the interrupt handler routine.
When a level trigger port input interrupt is used to wake up the C33 PE Core from SLEEP
mode, assert the input signal until the clock supply has started. Edge trigger port input in-
terrupts can also used to cancel SLEEP mode. The active signal edge will be automatically
converted into an active level signal by the GPIO module and it keeps on active until the clock
supply has started.
The same problem may occur when the CPU wakes up from SLEEP mode by an NMI. No in-
terrupt will occur if the #NMI signal is negated before the clock is supplied.
• Before setting the S1C33L26 into SLEEP mode, the clock supply for the USB and LCDC must
be disabled.
• Be sure to disable the instruction and data caches before executing the halt or slp instruction.