MC68HC05P18 Datasheet, PDF (65/144 Pages) Freescale Semiconductor, Inc – Advance Information

7.4 Port B
Freescale Semiconductor, Inc.
Input/Output (I/O) Ports
Port B
Port B is a 3-bit bidirectional port which can share pins PB5–PB7 with
the serial input/output port (SIOP) communications subsystem. The port
B data register is located at address $0001 and its data direction register
(DDR) is located at address $0005. Reset does not affect the data
registers, but clears the DDRs, thereby setting all of the port pins to input
mode. Writing a logic 1 to a DDR bit sets the corresponding port pin to
output mode (see Figure 7-2).
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 11. Serial Input/Output Port (SIOP) for a
discussion of the SIOP subsystem.
READ $0005
WRITE $0005
RESET
WRITE $0001 ^(RST)
READ $0001
DATA DIRECTION
REGISTER BIT
DATA
REGISTER BIT
OUTPUT
I/O
PIN
INTERNAL
HC05
DATA BUS
Figure 7-2. Port B I/O Circuitry
MC68HC(8)05P18 — Rev. 2.0
MOTOROLA
Input/Output (I/O) Ports
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Advance Information
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