Freescale
4-4
MC68HC05B6
Rev. 4.1
INPUT/OUTPUT PORTS
4
a digital read of port D with levels other than VDD or VSS on the port D pins will result in greater
power dissipation during the read cycle.
As port D is an input-only port there is no DDR associated with it. Also, at power up or external
reset, the A/D converter is disabled, thus the port is configured as a standard input-only port.
Note:
It is recommended that all unused input ports and I/O ports be tied to an appropriate
logic level (i.e. either VDD or VSS).
4.5
Port registers
The following sections explain in detail the individual bits in the data and control registers
associated with the ports.
4.5.1
Port data registers A and B (PORTA and PORTB)
Each bit can be configured as input or output via the corresponding data direction bit in the port
data direction register (DDRx).
The state of the port data registers following reset is not defined.
4.5.2
Port data register C (PORTC)
Each bit can be configured as input or output via the corresponding data direction bit in the port
data direction register (DDRx).
In addition, bit 2 of port C is used to output the CPU clock if the ECLK bit in the EEPROM
The state of the port data registers following reset is not defined.
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Port A data (PORTA)
$0000
Undefined
Port B data (PORTB)
$0001
Undefined
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Port C data (PORTC)
$0002
PC2/
ECLK
Undefined