COP8SA Datasheet, PDF (26/60 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based and One-Time Programmable OTP Microcontroller with 1k to 4k Memory, Power On Reset, and Very Small Packaging

8.0 Power Save Modes (Continued)
8.3 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 20 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 register WKEN. The regis-
ter WKEN is an 8-bit read/write register, which contains a
control bit for every L port bit. Setting a particular WKEN bit
enables 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 register 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
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
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 be-
ing 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:
RBIT
SBIT
RBIT
SBIT
5, WKEN
5, WKEDG
5, WKPND
5, WKEN
; Disable MIWU
; Change edge polarity
; Reset pending flag
; Enable MIWU
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 wakeup condi-
tions. After the selected L port bits have been changed from
output to input but before the associated WKEN bits are en-
abled, the associated edge select bits in WKEDG should be
set or reset for the desired edge selects, followed by the as-
sociated 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 must
clear the pending flags before attempting to enter the HALT
mode.
WKEN and WKEDG are all read/write registers, and are
cleared at reset. WKPND register contains random value af-
ter reset.
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FIGURE 20. Multi-Input Wake Up Logic
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