COP8SA National Semiconductor, COP8SA Datasheet - Page 24

• Manufacturer Part Number: COP8SA
• Description: 8-Bit CMOS ROM Based and One-Time Programmable OTP Microcontroller with 1k to 4k Memory/ Power On Reset/ and Very Small Packaging
• Manufacturer: National Semiconductor

www.national.com
8.0 Power Save Modes
Today, the proliferation of battery-operated based applica-
tions has placed new demands on designers to drive power
consumption down. Battery-operated systems are not the
only type of applications demanding low power. The power
budget constraints are also imposed on those consumer/
industrial applications where well regulated and expensive
power supply costs cannot be tolerated. Such applications
rely on low cost and low power supply voltage derived di-
rectly from the “mains” by using voltage rectifier and passive
components. Low power is demanded even in automotive
applications, due to increased vehicle electronics content.
This is required to ease the burden from the car battery. Low
power 8-bit microcontrollers supply the smarts to control
battery-operated, consumer/industrial, and automotive appli-
cations.
The COP8SAx devices offer system designers a variety of
low-power consumption features that enable them to meet
the demanding requirements of today’s increasing range of
low-power applications. These features include low voltage
operation, low current drain, and power saving features such
as HALT, IDLE, and Multi-Input wakeup (MIWU).
The devices offer the user two power save modes of opera-
tion: HALT and IDLE. In the HALT mode, all microcontroller
activities are stopped. In the IDLE mode, the on-board oscil-
lator circuitry and timer T0 are active but all other microcon-
troller activities are stopped. In either mode, all on-board
RAM, registers, I/O states, and timers (with the exception of
T0) are unaltered.
Clock Monitor if enabled can be active in both modes.
8.1 HALT MODE
The device can be placed in the HALT mode by writing a “1”
to the HALT flag (G7 data bit). All microcontroller activities,
including the clock and timers, are stopped. The WATCH-
DOG logic on the device is disabled during the HALT mode.
However, the clock monitor circuitry, if enabled, remains ac-
tive and will cause the WATCHDOG output pin (WDOUT) to
go low. If the HALT mode is used and the user does not want
to activate the WDOUT pin, the Clock Monitor should be dis-
abled after the device comes out of reset (resetting the Clock
Monitor control bit with the first write to the WDSVR register).
In the HALT mode, the power requirements of the device are
minimal and the applied voltage (V
V
The device supports three different ways of exiting the HALT
mode. The first method of exiting the HALT mode is with the
Multi-Input Wakeup feature on Port L. The second method is
r
(V
r
= 2.0V) without altering the state of the machine.
CC
) may be decreased to
24
with a low to high transition on the CKO (G7) pin. This
method precludes the use of the crystal clock configuration
(since CKO becomes a dedicated output), and so may only
be used with an R/C clock configuration. The third method of
exiting the HALT mode is by pulling the RESET pin low.
Since a crystal or ceramic resonator may be selected as the
oscillator, the Wakeup signal is not allowed to start the chip
running immediately since crystal oscillators and ceramic
resonators have a delayed start up time to reach full ampli-
tude and frequency stability. The IDLE timer is used to gen-
erate a fixed delay to ensure that the oscillator has indeed
stabilized before allowing instruction execution. In this case,
upon detecting a valid Wakeup signal, only the oscillator cir-
cuitry is enabled. The IDLE timer is loaded with a value of
256 and is clocked with the t
clock is derived by dividing the oscillator clock down by a fac-
tor of 10. The Schmitt trigger following the CKI inverter on
the chip ensures that the IDLE timer is clocked only when the
oscillator has a sufficiently large amplitude to meet the
Schmitt trigger specifications. This Schmitt trigger is not part
of the oscillator closed loop. The start-up time-out from the
IDLE timer enables the clock signals to be routed to the rest
of the chip.
If an R/C clock option is being used, the fixed delay is intro-
duced optionally. A control bit, CLKDLY, mapped as configu-
ration bit G7, controls whether the delay is to be introduced
or not. The delay is included if CLKDLY is set, and excluded
if CLKDLY is reset. The CLKDLY bit is cleared on reset.
The device has two options associated with the HALT mode.
The first option enables the HALT mode feature, while the
second option disables the HALT mode selected through bit
0 of the ECON register. With the HALT mode enable option,
the device will enter and exit the HALT mode as described
above. With the HALT disable option, the device cannot be
placed in the HALT mode (writing a “1” to the HALT flag will
have no effect, the HALT flag will remain “0”).
The WATCHDOG detector circuit is inhibited during the
HALT mode. However, the clock monitor circuit if enabled re-
mains active during HALT mode in order to ensure a clock
monitor error if the device inadvertently enters the HALT
mode as a result of a runaway program or power glitch.
If the device is placed in the HALT mode, with the R/C oscil-
lator selected, the clock input pin (CKI) is forced to a logic
high internally. With the crystal or external oscillator the CKI
pin is TRI-STATE.
C
instruction cycle clock. The t
C