mc68hc908kx8 Freescale Semiconductor, Inc, mc68hc908kx8 Datasheet - Page 109

• Manufacturer Part Number: mc68hc908kx8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

TxD — SCI Transmit Data Output Bit
AD3–AD0 — Analog-to-Digital Input Bits
11.3.2 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 11-8
Freescale Semiconductor
The PTB0/TxD pin is the transmit data output for the SCI module. When the enable SCI bit, ENSCI, is
clear, the SCI module is disabled, and the PTB0/TxD pin is available for general-purpose I/O. See
Chapter 12 Serial Communications Interface Module
AD3–AD0 are pins used for the input channels to the analog-to-digital converter (ADC) module. The
channel select bits in the ADC status and control register define which port B pin will be used as an
ADC input and overrides any control from the port I/O logic by forcing that pin as the input to the analog
circuitry. See
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
shows the port B I/O logic.
Address: $0005
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.
Reset:
Read:
Write:
Chapter 3 Analog-to-Digital Converter
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
READ DDRB ($0005)
WRITE DDRB ($0005)
WRITE PTB ($0001)
READ PTB ($0001)
DDRB7
Bit 7
0
Figure 11-7. Data Direction Register B (DDRB)
DDRB6
6
0
RESET
Figure 11-8. Port B I/O Circuit
DDRB5
5
0
NOTE
DDRB4
DDRBx
PTBx
4
0
(ADC).
(SCI).
DDRB3
3
0
DDRB2
2
0
DDRB1
1
0
DDRB0
Bit 0
PTBx
0
Port B
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