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CHAPTER 5 I/O PORTS
5.1
Overview of I/O Ports
This section provides I/O port block diagrams for the device and an outline of
registers.
I I/O port block diagrams
The MB91150 supports using a pin as an I/O port when the pin is not set to be used for input or
output of the resource corresponding to the pin.
When a pin is set to be used as input port, the level of the pin is read as the read value of the
port (PDR). When a pin is set to be used as output port, the value of a data register is used as
read value. This applies also to the read value for read modify write operations.
Before the pin setting is changed from input to output, the output data must be specified in
advance in the respective data register. Note that if an instruction of the read modify write
system (such as a bit set) is used in this situation, the data to be read is input data from a pin
instead of the latch value of the data register.
The MB91150 has the following types of I/O ports:
•
Basic I/O port
•
I/O port with pull-up resistor
•
I/O port with open-drain output function and pull-up resistor
•
I/O port with open-drain output function
I I/O port registers
The I/O ports are configured with the following registers:
•
Port data register (PDR)
•
Data direction register (DDR)
•
Pull-up resistor control register (PCR)
•
Open-drain control register (ODCR)
•
Analog input control register (AICR)
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