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Serial Communication Modules
MOTOROLA
MPC801 USER’S MANUAL
16-35
16
F—Full Mask
If this bit is set to 1, the corresponding interrupt in the I2CER is enabled. If it is zero, the
interrupt is masked.
E—Empty Mask
If this bit is set to 1, the corresponding interrupt in the I2CER is enabled. If it is zero, the
interrupt is masked.
16.4 THE PARALLEL I/O PORT
The MPC801 supports a general-purpose I/O port. Each pin in the I/O port can be configured
as a general-purpose I/O pin or a dedicated peripheral interface pin. Port B is shared with
the serial peripheral interface, I
2
C, and the UART1 and UART2 pins. Each pin can be
configured as an input or output and has a latch for data output. They can be read or written
to at any time. Port B pins can be configured as open-drain (configured in a wired-OR
configuration) on the board. The pin drives a zero voltage, but three-states when driving a
high voltage.
NOTE
The port pins do not have internal pull-up resistors.
16.4.1 Features
The following is a list of the parallel I/O port’s main features:
16 Bits Wide
Open-Drain Capability
All Pins Are Bidirectional, Have Alternate On-Chip Peripheral Functions, and
Three-Stated at System Reset.
Pin Values are Readable While the Pin Is Connected to an On-Chip Peripheral
16.4.2 Port B Pin Functions
Port B pins are independently configured as general-purpose I/O pins if the corresponding
bit in the port B pin assignment register (PBPAR) is cleared. They are configured as
dedicated on-chip peripheral pins if the corresponding PBPAR and PBDIR bits are set.
When acting as a general-purpose I/O pin, the signal direction for that pin is determined by
the corresponding control bit in the port B data direction (PBDIR) register. The port I/O pin
is configured as an input if the corresponding PBDIR bit is cleared or as an output if the
corresponding PBDIR bit is set. All PBPAR and PBDIR bits are cleared at the time of total
system reset and all port B pins are configured as general-purpose input pins.