Справочник Пользователя для Intel 8XC196MC
8XC196MC, MD, MH USER’S MANUAL
6-10
To prevent the CMOS inputs from floating, the bidirectional port pins are weakly pulled high dur-
ing and after reset, until your software writes to Px_MODE. The default values of the control reg-
isters after reset configure the pins as high-impedance inputs with weak pull-ups. To ensure that
the ports are initialized correctly and that the weak pull-ups are turned off, follow this suggested
initialization sequence:
ing and after reset, until your software writes to Px_MODE. The default values of the control reg-
isters after reset configure the pins as high-impedance inputs with weak pull-ups. To ensure that
the ports are initialized correctly and that the weak pull-ups are turned off, follow this suggested
initialization sequence:
1.
Write to Px_DIR to establish the individual pins as either inputs or outputs. (Outputs will
drive the data that you specify in step 3.)
drive the data that you specify in step 3.)
— For a complementary output, clear its Px_DIR bit.
— For a high-impedance input or an open-drain output, set its Px_DIR bit. (Open-drain
outputs require external pull-ups.)
2.
Write to Px_MODE to select either I/O or special-function mode. Writing to Px_MODE
(regardless of the value written) turns off the weak pull-ups. Even if the entire port is to be
used as I/O (its default configuration after reset), you must write to Px_MODE to ensure
that the weak pull-ups are turned off.
(regardless of the value written) turns off the weak pull-ups. Even if the entire port is to be
used as I/O (its default configuration after reset), you must write to Px_MODE to ensure
that the weak pull-ups are turned off.
— For a standard I/O pin, clear its Px_MODE bit. In this mode, the pin is driven as
defined in steps 1 and 3.
— For a special-function signal, set its Px_MODE bit. In this mode, the associated
peripheral controls the pin.
3.
Write to Px_REG.
— For output pins defined in step 1, write the data that is to be driven by the pins to the
corresponding Px_REG bits. For special-function outputs, the value is immaterial
because the peripheral controls the pin. However, you must still write to Px_REG to
initialize the pin.
because the peripheral controls the pin. However, you must still write to Px_REG to
initialize the pin.
— For input pins defined in step 1, set the corresponding Px_REG bits.
Table 6-8 lists the control register values for each possible configuration. For special-function
outputs, the Px_REG value is irrelevant (don’t care) because the associated peripheral controls
the pin in special-function mode. However, you must still write to Px_REG to initialize the pin.
For a bidirectional pin to function as an input (either special function or port pin), you must set
Px_REG.
outputs, the Px_REG value is irrelevant (don’t care) because the associated peripheral controls
the pin in special-function mode. However, you must still write to Px_REG to initialize the pin.
For a bidirectional pin to function as an input (either special function or port pin), you must set
Px_REG.