MC68HC908AS60ACFN FREESCALE [Freescale Semiconductor, Inc], MC68HC908AS60ACFN Datasheet - Page 253

• Manufacturer Part Number: MC68HC908AS60ACFN
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

22.3.2 Data Direction Register B
Data direction register B 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.
DDRB[7:0] — Data Direction Register B Bits
Figure 22-7
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.
Freescale Semiconductor
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
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
shows the port B I/O logic.
DDRB
Address:
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.
Bit
0
1
Reset:
Read:
Write:
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
READ DDRB ($0005)
WRITE DDRB ($0005)
WRITE PTB ($0001)
READ PTB ($0001)
DDRB7
$0005
Bit 7
0
PTB
Bit
Figure 22-6. Data Direction Register B (DDRB)
X
X
DDRB6
6
0
Table 22-2. Port B Pin Functions
RESET
Figure 22-7. Port B I/O Circuit
Input, Hi-Z
I/O Pin
Output
Mode
DDRB5
5
0
Table 22-2
NOTE
Accesses to DDRB
DDRB4
DDRBx
PTBx
4
0
Read/Write
DDRB[7:0]
DDRB[7:0]
summarizes the operation of the port B pins.
DDRB3
3
0
DDRB2
2
0
PTB[7:0]
Read
Pin
Accesses to PTB
DDRB1
1
0
PTB[7:0]
PTB[7:0]
Write
DDRB0
Bit 0
PTBx
0
(1)
Port B
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