Power-Down Control - Epson S1C33210 Technical Manual

5 POWER-DOWN CONTROL

5 Power-Down Control
This chapter describes the controls used to reduce power consumption of the device.
Points on power saving
The current consumption of the device varies greatly with the CPU's operation mode, the system clocks used,
and the peripheral circuits operated.
Current consumption
CPU/BCU
System clock
OSC3 oscillation circuit
Prescaler/peripheral circuit
To reduce power consumption of the device, it is important that as many unnecessary circuits as possible be
turned off. In particular, peripheral circuits operating at a fast-clock rate consume a large amount of current, so
design the program so that these circuits are turned off whenever unnecessary.
Power-saving in standby modes
When CPU processing is unnecessary, such as when waiting for an interrupt from key entries or peripheral
circuits, place the device in standby mode to reduce current consumption.
Standby mode
Basic HALT mode Execute the halt instruction after setting
HALT2 mode
SLEEP mode
HLT2OP (D3)/Clock option register (0x40190) that is used to select a HALT mode is set to "0" (basic HALT
mode) at initial reset.
Notes: • In systems in which DRAM is connected directly to the device, the refresh function is turned off
during HALT2 and SLEEP modes.
• The standby mode is cleared by interrupt generation (except for the basic HALT mode, which is
set using an external bus master). Therefore, before entering standby mode, set the related
registers to allow an interrupt to be used to clear the standby mode to be generated.
• When clearing the standby mode with an interrupt from port input, the interrupt operates as a
level interrupt regardless of the interrupt trigger setting. When edge trigger is set for the interrupt
trigger, attention must be paid to the port level during standby mode.
The low-speed (OSC1) oscillation circuit and clock timer continue operating even during SLEEP mode. If they
are unnecessary, these circuits can also be turned off.
Function
Low-speed (OSC1) oscillation ON/OFF control
A-62
low
SLEEP HALT2
–
OFF
STOP
Method to enter the mode
HLT2OP (D3)/Clock option register
(0x40190) to "0".
When the #BUSREQ signal is asserted from
an external bus master while SEPD (D1)/Bus
control register (0x4812E) = "1".
Execute the halt instruction after setting
HLT2OP to "1".
Execute the slp instruction.
Operating
OSC1 OSC1
OFF OFF
CPU and DMA
CPU, BCU, bus clock, and DMA
CPU, BCU, bus clock, DMA, high-speed
(OSC3) oscillation circuit, prescaler, and
peripheral circuits that use the prescaler
output clocks
Control bit
SOSC1(D0)/
Power control register(0x40180)
EPSON
HALT2 HALT(basic)
OSC3 OSC3
ON ON
Circuits/functions stopped
"1" "0"
ON OFF
S1C33210 PRODUCT PART
high
Operating
OSC3
ON
RUN
Default
ON