MC68HC05C8A Datasheet, PDF (56/158 Pages) Motorola, Inc – Microcontrollers

Input/Output (I/O) Ports
7.3 Port A
Port A is an 8-bit bidirectional port which does not share any of its pins
with other subsystems. The port A data register is at $0000 and the data
direction register (DDR) is at $0004. Reset does not affect the data
registers, but clears the data direction registers, thereby returning the
ports to inputs. Writing a 1 to a DDR bit sets the corresponding port bit
to output mode.
7.4 Port B
Port B is an 8-bit bidirectional port. The port B data register is at $0001
and the data direction register (DDR) is at $0005. Reset does not affect
the data registers, but clears the data direction registers, thereby
returning the ports to inputs. Writing a 1 to a DDR bit sets the
corresponding port pin to output mode. Each of the port B pins has a
mask programmable interrupt capability. This interrupt option also
enables a pullup device when the pin is configured as an input (see
Figure 7-1). The edge or edge and level sensitivity of the IRQ pin also
will pertain to the enabled port B pins via mask options. Be careful when
using port B pins that have the pullup enabled. Before switching from an
output to an input, the data should be preconditioned to a 1 to prevent
an interrupt from occurring.
V_DD
V_DD
MASK OPTION
DDR BIT
PB0
NORMAL PORT CIRCUITRY
AS SHOWN IN
FIGURE 7-2
IRQ
SCHMITT
TRIGGER
FROM ALL OTHER PORT B PINS
Figure 7-1. Port B Pullup Option
TO INTERRUPT
LOGIC
Technical Data
56
MC68HC05C8A • MC68HCL05C8A • MC68HSC05C8A — Rev. 5.0
Input/Output (I/O) Ports
MOTOROLA