
Input/Output Ports (PORTS)
Port B
MC68HC908QY/QT Family — Rev. 3
Data Sheet
MOTOROLA
Input/Output Ports (PORTS)
109
12.3 Port B
Port B is an 8-bit general purpose I/O port. Port B is only available on the
MC68HC908QY1, MC68HC908QY2, and MC68HC908QY4.
12.3.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the eight port B
pins.
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.
12.3.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or
an output. Writing a 1 to a DDRB bit enables the output buffer for the corresponding
port B pin; a 0 disables the output buffer.
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. Figure 12-8 shows the port B I/O logic.
Address: $0001
Bit 7
6
54
32
1
Bit 0
Read:
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Write:
Reset:
Unaffected by reset
Figure 12-6. Port B Data Register (PTB)
Address: $0005
Bit 7
6
54
32
1
Bit 0
Read:
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
Write:
Reset:
000
00
000
Figure 12-7. Data Direction Register B (DDRB)
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Freescale Semiconductor, Inc.
For More Information On This Product,
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