MC68HC705 MOTOROLA [Motorola, Inc], MC68HC705 Datasheet - Page 78

• Manufacturer Part Number: MC68HC705
• Description: HCMOS Microcontroller Unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Parallel Input/Output (I/O)
7.3.3 Port A Logic
Technical Data
78
NOTE:
Figure 7-3
When a port A pin is programmed to be an output, the state of its data
register bit determines the state of the output pin. When a port A pin is
programmed to be an input, reading the port A data register returns the
logic state of the pin.
The data latch can always be written, regardless of the state of its DDRA
bit.
To avoid excessive current draw, tie all unused input pins to V
or change I/O pins to outputs by writing to DDRA in user code as early
as possible.
1. Hi-Z = high impedance
2. Writing affects data register but does not affect input.
DDRA Bit
Table 7-1
0
1
READ $0004
WRITE $0004
WRITE $0000
READ $0000
is a diagram of the port A I/O logic.
Parallel Input/Output (I/O)
I/O Pin Mode
Input, Hi-Z
summarizes the operation of the port A pins.
RESET
Output
Table 7-1. Port A Pin Functions
Figure 7-3. Port A I/O Logic
(1)
DATA DIRECTION
PORT A DATA
REGISTER A
REGISTER
BIT DDRAx
BIT PAx
Accesses to DDRA
DDRA7–DDRA0
DDRA7–DDRA0
Read/Write
MC68HC705C8A — Rev. 2.0
PA7–PA0
Accesses to PORTA
Read
Pin
PA7–PA0
MOTOROLA
DD
PA7–PA0
Write
or V
PAx
(2)
SS
,