s908gr16ag4cfj Freescale Semiconductor, Inc, s908gr16ag4cfj Datasheet - Page 121

• Manufacturer Part Number: s908gr16ag4cfj
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

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.
DDRB7–DDRB0 — Data Direction Register B Bits
Figure 12-8
When bit DDRBx is a 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a 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.
Freescale Semiconductor
1. X = Don’t care
2. Hi-Z = High impedance
3. Writing affects data register, but does not affect input.
These read/write bits control port B data direction. Reset clears DDRB7–DDRB0, configuring all port
B pins as inputs.
DDRB
Bit
0
1
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
shows the port B I/O logic.
PTB
Address:
X
Bit
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.
X
(1)
Reset:
Read:
Write:
READ DDRB ($0005)
WRITE DDRB ($0005)
WRITE PTB ($0001)
READ PTB ($0001)
DDRB7
$0005
Bit 7
Input, Hi-Z
0
I/O Pin
Output
Figure 12-7. Data Direction Register B (DDRB)
Mode
DDRB6
(2)
6
0
MC68HC908GR16A Data Sheet, Rev. 1.0
Table 12-3. Port B Pin Functions
RESET
Figure 12-8. Port B I/O Circuit
DDRB5
5
0
Accesses to DDRB
DDRB7–DDRB0
DDRB7–DDRB0
Table 12-3
Read/Write
NOTE
DDRB4
DDRBx
PTBx
4
0
summarizes the operation of the port B pins.
DDRB3
3
0
DDRB2
PTB7–PTB0
2
0
Read
Pin
DDRB1
Accesses to PTB
1
0
DDRB0
Bit 0
PTBx
0
PTB7–PTB0
PTB7–PTB0
Write
(3)
Port B
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