MC68HC08LT8 Datasheet, PDF (97/156 Pages) Freescale Semiconductor, Inc – Microcontrollers

Port A
9.2.2 Data Direction Register A (DDRA)
Data direction register A determines whether each port A pin is an input or an output. Writing a logic 1 to
a DDRA bit enables the output buffer for the corresponding port A pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0004
Bit 7
6
5
4
3
2
1
DDRA7 DDRA6 DDRA5 DDRA4 DDRA3 DDRA2 DDRA1
0
0
0
0
0
0
0
Figure 9-3. Data Direction Register A (DDRA)
Bit 0
DDRA0
0
DDRA[7:0] — Data Direction Register A Bits
These read/write bits control port A data direction. Reset clears DDRA[7:0], configuring all port A pins
as inputs.
1 = Corresponding port A pin configured as output
0 = Corresponding port A pin configured as input
NOTE
Avoid glitches on port A pins by writing to the port A data register before
changing data direction register A bits from 0 to 1. Figure 9-4 shows the port
A I/O logic.
READ DDRA ($0004)
WRITE DDRA ($0004)
RESET
DDRAx
WRITE PTA ($0000)
PTAx
PTAx
READ PTA ($0000)
Figure 9-4. Port A I/O Circuit
When DDRAx is a logic 1, reading address $0000 reads the PTAx data latch. When DDRAx is a logic 0,
reading address $0000 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 9-2 summarizes the operation of the port A pins.
Table 9-2. Port A Pin Functions
DDRA
Bit
PTA Bit
I/O Pin Mode
Accesses to DDRA
Read/Write
0
X⁽¹⁾
Input, Hi-Z⁽²⁾
DDRA[7:0]
1
X
Output
DDRA[7:0]
1. X = don’t care.
2. Hi-Z = high impedance.
3. Writing affects data register, but does not affect input.
Accesses to PTA
Read
Write
Pin
PTA[7:0]⁽³⁾
PTA[7:0]
PTA[7:0]
MC68HC08LT8 Data Sheet, Rev. 1
Freescale Semiconductor
97