
Technical Data
MC68HC11E Family
—
Rev. 4
42
Pin Descriptions
MOTOROLA
Pin Descriptions
2.13.3 Port C
While in single-chip operating modes, all port C pins are
general-purpose I/O pins. Port C inputs can be latched into an alternate
PORTCL register by providing an input transition to the STRA signal.
Port C can also be used in full handshake modes of parallel I/O where
the STRA input and STRB output act as handshake control lines.
When in expanded multiplexed modes, all port C pins are configured as
multiplexed address/data signals. During the address portion of each
MCU cycle, bits 7
–
0 of the address are output on the PC7
–
PC0 pins.
During the data portion of each MCU cycle (E high), PC7
–
PC0 are
bidirectional data signals, DATA7
–
DATA0. The direction of data at the
port C pins is indicated by the R/W signal.
The CWOM control bit in the PIOC register disables the port C P-channel
output driver. CWOM simultaneously affects all eight bits of port C.
Because the N-channel driver is not affected by CWOM, setting CWOM
causes port C to become an open-drain type output port suitable for
wired-OR operation.
In wired-OR mode:
When a port C bit is at logic level 0, it is driven low by the
N-channel driver.
When a port C bit is at logic level 1, the associated pin has
high-impedance, as neither the N-channel nor the P-channel
devices are active.
It is customary to have an external pullup resistor on lines that are driven
by open-drain devices. Port C can only be configured for wired-OR
operation when the MCU is in single-chip mode. Refer to
Section 6.
Parallel Input/Output (I/O) Ports
for additional information about port C
functions.