Reducing Power Consumption - Intel 8XC196MC User Manual

Table 14-2. Operating Mode Control and Status Registers (Continued)
Mnemonic
P1_DIR (MH) 1F9BH
P2_DIR 1FD2H
P5_DIR 1FF3H
P7_DIR (MD) 1FD3H
P1_MODE(MH) 1F99H
P2_MODE 1FD0H
P5_MODE 1FF1H
P7_MODE(MD) 1FD1H
P1_REG (MH) 1F9DH
P2_REG 1FD4H
P5_REG 1FF5H
P7_REG (MD) 1FD5H

14.2 REDUCING POWER CONSUMPTION

Both power-saving modes conserve power by disabling portions of the internal clock circuitry
(Figure 14-1). The following paragraphs describe both modes in detail.
Address
Port x Direction
Each bit of P x _DIR controls the direction of the corresponding pin.
Clearing a bit configures a pin as a complementary output; setting
a bit configures a pin as an input or open-drain output. (Open-
drain outputs require external pull-ups.)
Port x Mode
Each bit of P x _MODE controls whether the corresponding pin
functions as a standard I/O port pin or as a special-function
signal. Setting a bit configures a pin as a special-function signal;
clearing a bit configures a pin as a standard I/O port pin.
Port x Data Output
For an input, set the corresponding P x _REG bit.
For an output, write the data to be driven out by each pin to the
corresponding bit of P x _REG. When a pin is configured as
standard I/O (P x _MODE. y = 0), the result of a CPU write to
P x _REG is immediately visible on the pin. When a pin is
configured as a special-function signal (P x _MODE. y = 1), the
associated on-chip peripheral or off-chip component controls the
pin. The CPU can still write to P x _REG, but the pin is unaffected
until it is switched back to its standard I/O function.
This feature allows software to configure a pin as standard I/O
(clear P x _MODE. y ), initialize or overwrite the pin value, then
configure the pin as a special-function signal (set P x _MODE. y ). In
this way, initialization, fault recovery, exception handling, etc., can
be done without changing the operation of the associated
peripheral.
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SPECIAL OPERATING MODES
Description
14-3