Motorola MC68HC05RC8 User Manual
Parallel Input/Output (I/O)
General Release Specification
MC68HC05RC16 — Rev. 3.0
58
Parallel Input/Output (I/O)
MOTOROLA
7.4 Port B
Port B is an 8-bit bidirectional port which does not share any of its pins
with other subsystems. The address of the port B data register is $0001
and the data direction register (DDR) is at address $0005. Reset does
not affect the data register, but clears the data direction register, thereby
returning the ports to inputs. Writing a one to a DDR bit sets the
corresponding port bit to output mode. Each of the port B pins has a
mask programmable pullup device that can be enabled. When the pullup
device is enabled, this pin will become an interrupt pin also. The edge or
edge and level sensitivity of the IRQ pin also will pertain to the enabled
port B pins. Care needs to be taken 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 logic one or the I bit should be set in the
condition code register to prevent an interrupt from occurring. The
EIMSK bit in the CMT MCSR register can be used to mask port B
keyscan and external interrupts (IRQ).
with other subsystems. The address of the port B data register is $0001
and the data direction register (DDR) is at address $0005. Reset does
not affect the data register, but clears the data direction register, thereby
returning the ports to inputs. Writing a one to a DDR bit sets the
corresponding port bit to output mode. Each of the port B pins has a
mask programmable pullup device that can be enabled. When the pullup
device is enabled, this pin will become an interrupt pin also. The edge or
edge and level sensitivity of the IRQ pin also will pertain to the enabled
port B pins. Care needs to be taken 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 logic one or the I bit should be set in the
condition code register to prevent an interrupt from occurring. The
EIMSK bit in the CMT MCSR register can be used to mask port B
keyscan and external interrupts (IRQ).
NOTE:
When a port B pin is configured as an output, it’s corresponding keyscan
interrupt is disabled, regardless of it’s mask option.
interrupt is disabled, regardless of it’s mask option.
Figure 7-1. Port B Pullup Option
7.5 Port C
Port C is an 8-bit bidirectional port (PC0–PC7) which does not share any
of its pins with other subsystems. The port C data register is at $0003
and the data direction register (DDR) is at $0006. Reset does not affect
the data register, but clears the data direction register, thereby returning
of its pins with other subsystems. The port C data register is at $0003
and the data direction register (DDR) is at $0006. Reset does not affect
the data register, but clears the data direction register, thereby returning
PB7
V
DD
V
DD
DDR BIT
NORMAL PORT CIRCUITRY
AS SHOWN IN FIGURE 7-2
IRQ
TO INTERRUPT
LOGIC
MASK OPTION (PB7PU)
DISABLED
ENABLED
FROM ALL OTHER PORT B PINS
IRQEN