MC908AZ32ACFUE Datasheet, PDF (251/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Port D
23.5.2 Data Direction Register D
Data direction register D determines whether each port D pin is an input or an output. Writing a logic 1 to
a DDRD bit enables the output buffer for the corresponding port D pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0007
Bit 7
DDRD7
0
6
DDRD6
0
5
DDRD5
0
4
DDRD4
0
3
DDRD3
0
2
DDRD2
0
1
DDRD1
0
Bit 0
DDRD0
0
Figure 23-12. Data Direction Register D (DDRD)
DDRD[7:0] — Data Direction Register D Bits
These read/write bits control port D data direction. Reset clears DDRD[7:0], configuring all port D pins
as inputs.
1 = Corresponding port D pin configured as output
0 = Corresponding port D pin configured as input
NOTE
Avoid glitches on port D pins by writing to the port D data register before
changing data direction register D bits from 0 to 1.
Figure 23-13 shows the port D I/O logic.
READ DDRD ($0007)
WRITE DDRD ($0007)
RESET
WRITE PTD ($0003)
DDRDx
PTDx
PTDx
READ PTD ($0003)
Figure 23-13. Port D I/O Circuit
When bit DDRDx is a logic 1, reading address $0003 reads the PTDx data latch. When bit DDRDx is a
logic 0, reading address $0003 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-4 summarizes the operation of the port D pins.
Table 23-4. Port D Pin Functions
DDRD PTD
Bit
Bit
I/O Pin
Mode
Accesses to
DDRD
Read/Write
0
X
Input, Hi-Z
DDRD[7:0]
1
X
Output
DDRD[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
Accesses to PTD
Read
Pin
PTD[7:0]
Write
PTD[7:0]⁽¹⁾
PTD[7:0]
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
251