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Pin Descriptions
Port Signals
MC68HC11E Family — Rev. 4
Technical Data
MOTOROLA
Pin Descriptions
39
indicates that a read cycle is in progress. R/W stays low during
consecutive data bus write cycles, such as a double-byte store. It is
possible for data to be driven out of port C, if internal read visibility (IRV)
is enabled and an internal address is read, even though R/W is in a
visibility not E).
2.13 Port Signals
Port pins have different functions in different operating modes. Pin
functions for port A, port D, and port E are independent of operating
modes. Port B and port C, however, are affected by operating mode.
Port B provides eight general-purpose output signals in single-chip
operating modes. When the microcontroller is in expanded multiplexed
operating mode, port B pins are the eight high-order address lines.
Port C provides eight general-purpose input/output signals when the
MCU is in the single-chip operating mode. When the microcontroller is in
the expanded multiplexed operating mode, port C pins are a multiplexed
address/data bus.
Refer to Table 2-1 for a functional description of the 40 port signals
within different operating modes. Terminate unused inputs and
input/output (I/O) pins configured as inputs high or low.
2.13.1 Port A
In all operating modes, port A can be configured for three timer input
capture (IC) functions and four timer output compare (OC) functions. An
additional pin can be configured as either the fourth IC or the fifth OC.
Any port A pin that is not currently being used for a timer function can be
used as either a general-purpose input or output line. Only port A pins
PA7 and PA3 have an associated data direction control bit that allows
the pin to be selectively configured as input or output. Bits DDRA7 and
DDRA3 located in PACTL register control data direction for PA7 and
PA3, respectively. All other port A pins are fixed as either input or output.