cop888cf National Semiconductor Corporation, cop888cf Datasheet - Page 20

• Manufacturer Part Number: cop888cf
• Description: 8-bit Cmos Rom Based Microcontrollers With 4k Memory And A/d Converter
• Manufacturer: National Semiconductor Corporation

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Power Save Modes
IDLE MODE
The device is placed in the IDLE mode by writing a “1” to the
IDLE flag (G6 data bit). In this mode, all activity, except the
associated on-board oscillator circuitry, the WatchDog logic,
the clock monitor and the IDLE Timer T0, is stopped.
As with the HALT mode, the device can be returned to nor-
mal operation with a reset, or with a Multi-Input Wakeup from
the L Port. Alternately, the microcontroller resumes normal
operation from the IDLE mode when the thirteenth bit (repre-
senting 4.096 ms at internal clock frequency of 1 MHz,
t
This toggle condition of the thirteenth bit of the IDLE Timer
T0 is latched into the T0PND pending flag.
The user has the option of being interrupted with a transition
on the thirteenth bit of the IDLE Timer T0. The interrupt can
be enabled or disabled via the T0EN control bit. Setting the
T0EN flag enables the interrupt and vice versa.
The user can enter the IDLE mode with the Timer T0 inter-
rupt enabled. In this case, when the T0PND bit gets set, the
device will first execute the Timer T0 interrupt service routine
and then return to the instruction following the “Enter Idle
Mode” instruction.
Alternatively, the user can enter the IDLE mode with the
IDLE Timer T0 interrupt disabled. In this case, the device will
resume normal operation with the instruction immediately
following the “Enter IDLE Mode” instruction.
Note: It is necessary to program two NOP instructions following both the set
Multi-Input Wakeup
The Multi-Input Wakeup feature is used to return (wakeup)
the device from either the HALT or IDLE modes. Alternately
Multi-Input Wakeup/Interrupt feature may also be used to
generate up to 8 edge selectable external interrupts.
Figure 11 shows the Multi-Input Wakeup logic.
The Multi-Input Wakeup feature utilizes the L Port. The user
selects which particular L port bit (or combination of L Port
bits) will cause the device to exit the HALT or IDLE modes.
The selection is done through the Reg: WKEN. The Reg:
WKEN is an 8-bit read/write register, which contains a con-
trol bit for every L port bit. Setting a particular WKEN bit en-
ables a Wakeup from the associated L port pin.
The user can select whether the trigger condition on the se-
lected L Port pin is going to be either a positive edge (low to
high transition) or a negative edge (high to low transition).
This selection is made via the Reg: WKEDG, which is an
8-bit control register with a bit assigned to each L Port pin.
Setting the control bit will select the trigger condition to be a
c
= 1 µs) of the IDLE Timer toggles.
HALT mode and set IDLE mode instructions. These NOP instructions
are necessary to allow clock resynchronization following the HALT or
IDLE modes.
(Continued)
20
negative edge on that particular L Port pin. Resetting the bit
selects the trigger condition to be a positive edge. Changing
an edge select entails several steps in order to avoid a
pseudo Wakeup condition as a result of the edge change.
First, the associated WKEN bit should be reset, followed by
the edge select change in WKEDG. Next, the associated
WKPND bit should be cleared, followed by the associated
WKEN bit being re-enabled.
An example may serve to clarify this procedure. Suppose we
wish to change the edge select from positive (low going high)
to negative (high going low) for L Port bit 5, where bit 5 has
previously been enabled for an input interrupt. The program
would be as follows:
If the L port bits have been used as outputs and then
changed to inputs with Multi-Input Wakeup/Interrupt, a safety
procedure should also be followed to avoid inherited pseudo
wakeup conditions. After the selected L port bits have been
changed from output to input but before the associated
WKEN bits are enabled, the associated edge select bits in
WKEDG should be set or reset for the desired edge selects,
followed by the associated WKPND bits being cleared.
This same procedure should be used following reset, since
the L port inputs are left floating as a result of reset.
The occurrence of the selected trigger condition for
Multi-Input Wakeup is latched into a pending register called
WKPND. The respective bits of the WKPND register will be
set on the occurrence of the selected trigger edge on the cor-
responding Port L pin. The user has the responsibility of
clearing these pending flags. Since WKPND is a pending
register for the occurrence of selected wakeup conditions,
the device will not enter the HALT mode if any Wakeup bit is
both enabled and pending. Consequently, the user has the
responsibility of clearing the pending flags before attempting
to enter the HALT mode.
The WKEN, WKPND and WKEDG are all read/write regis-
ters, and are cleared at reset.
PORT L INTERRUPTS
Port L provides the user with an additional eight fully select-
able, edge sensitive interrupts which are all vectored into the
same service subroutine.
The interrupt from Port L shares logic with the wake up cir-
cuitry. The register WKEN allows interrupts from Port L to be
individually enabled or disabled. The register WKEDG speci-
fies the trigger condition to be either a positive or a negative
edge. Finally, the register WKPND latches in the pending
trigger conditions.
RBIT 5, WKEN
SBIT 5, WKEDG
RBIT 5, WKPND
SBIT 5, WKEN
; Disable MIWU
; Change edge polarity
; Reset pending flag
; Enable MIWU