Freescale Semiconductor MC68HC908MR32 - Manual (Page 103)

Port A
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 103
10.2 Port A
Port A is an 8-bit, general-purpose, bidirectional I/O port.
10.2.1 Port A Data Register
The port A data register (PTA) contains a data latch for each of the eight port A pins.
PTA[7:0] — Port A Data Bits
These read/write bits are software programmable. Data direction of each port A pin is under the control
of the corresponding bit in data direction register A. Reset has no effect on port A data.
10.2.2 Data Direction Register A
Data direction register A (DDRA) 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.
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 10-4 shows the port A I/O logic.
Address: $0000
Bit 7 6 5 4 3 2 1 Bit 0
Read:
PTA7 PTA6 PTA5 PTA4 PTA3 PTA2 PTA1 PTA0
Write:
Reset: Unaffected by reset
Figure 10-2. Port A Data Register (PTA)
Address: $0004
Bit 7 6 5 4 3 2 1 Bit 0
Read:
DDRA7 DDRA6 DDRA5 DDRA4 DDRA3 DDRA2 DDRA1 DDRA0
Write:
Reset: 0 0 0 0 0 0 0 0
Figure 10-3. Data Direction Register A (DDRA)