Input/Output (I/O) Ports (PORTS)
Port B
10.3 Port B
Port B is an 8-bit, general-purpose, bidirectional I/O port that shares its pins with
the analog-to-digital convertor (ADC) module.
10.3.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the eight port B
pins.
Address:
$0001
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Unaffected by reset
Figure 10-5. Port B Data Register (PTB)
PTB[7:0] — Port B Data Bits
These read/write bits are software-programmable. Data direction of each port B
pin is under the control of the corresponding bit in data direction register B.
Reset has no effect on port B data.
10.3.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or
an output. Writing a logic 1 to a DDRB bit enables the output buffer for the
corresponding port B pin; a logic 0 disables the output buffer.
Address:
$0005
Bit 7
6
DDRB6
0
5
DDRB5
0
4
DDRB4
0
3
DDRB3
0
2
DDRB2
0
1
DDRB1
0
Bit 0
DDRB0
0
Read:
Write:
Reset:
DDRB7
0
Figure 10-6. Data Direction Register B (DDRB)
DDRB[7:0] — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears DDRB[7:0],
configuring all port B pins as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
NOTE:
Avoid glitches on port B pins by writing to the port B data register before changing
data direction register B bits from 0 to 1.
MC68HC908MR32 • MC68HC908MR16 — Rev. 6.0
MOTOROLA Input/Output (I/O) Ports (PORTS)
Data Sheet
115
FREESCALE [ Freescale ]
