MC68HC705P6A Datasheet, PDF (53/130 Pages) Motorola, Inc – HCMOS Microcontroller Unit

6.4 Port B
Input/Output Ports
Port B
Port B is a 3-bit bidirectional port which can share pins PB5–PB7 with
the SIOP communications subsystem. The port B data register is located
at address $0001 and its data direction register (DDR) is located at
address $0005. The contents of the port B data register are
indeterminate at initial powerup and must be initialized by user software.
Reset does not affect the data registers, but clears the DDRs, thereby
setting all of the port pins to input mode. Writing a 1 to a DDR bit sets the
corresponding port pin to output mode (see Figure 6-2).
Port B may be used for general I/O applications when the SIOP
subsystem is disabled. The SPE bit in register SPCR is used to
enable/disable the SIOP subsystem. When the SIOP subsystem is
enabled, port B registers are still accessible to software. Writing to either
of the port B registers while a data transfer is under way could corrupt
the data. See Section 7. Serial Input/Output Port (SIOP) for a
discussion of the SIOP subsystem.
READ $0005
WRITE $0005
WRITE $0001
RESET
(RST)
DATA DIRECTION
REGISTER BIT
DATA
REGISTER BIT
I/O
OUTPUT
PIN
READ $0001
INTERNAL HC05
DATA BUS
Figure 6-2. Port B I/O Circuitry
MC68HC705P6A — Rev. 2.0
MOTOROLA
Input/Output Ports
Advance Information
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