MC68HC908GR16 Datasheet, PDF (135/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Input/Output Ports (PORTS)
Port B
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 logic 1 to a DDRB bit enables the output buffer for the
corresponding port B pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0005
Bit 7
6
5
4
3
2
1
DDRB7 DDRB6 DDRB5 DDRB4 DDRB3 DDRB2 DDRB1
0
0
0
0
0
0
0
Figure 12-7. Data Direction Register B (DDRB)
Bit 0
DDRB0
0
NOTE:
DDRB7–DDRB0 — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears
DDRB7–DDRB0, configuring all port B pins as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
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.
READ DDRB ($0005)
WRITE DDRB ($0005)
RESET
WRITE PTB ($0001)
DDRBx
PTBx
PTBx
READ PTB ($0001)
Figure 12-8. Port B I/O Circuit
When bit DDRBx is a logic 1, reading address $0001 reads the PTBx data latch.
When bit DDRBx is a logic 0, reading address $0001 reads the voltage level on the
pin. The data latch can always be written, regardless of the state of its data
direction bit. Table 12-3 summarizes the operation of the port B pins.
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Input/Output Ports (PORTS)
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Data Sheet
135