MC68HC908AS32A Datasheet, PDF (153/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Port B
13.3 Port B
Port B is an 8-bit special function port that shares all of its pins with the analog-to-digital converter (ADC).
13.3.1 Port B Data Register
The port B data register contains a data latch for each of the eight port B pins.
Address: $0001
Bit 7
Read:
PTB7
Write:
Reset:
Alternative Functions: ATD7
6
PTB6
ATD6
5
PTB5
ATD5
4
3
PTB4
PTB3
Unaffected by reset
ATD4
ATD3
2
PTB2
ATD2
Figure 13-4. Port B Data Register (PTB)
1
PTB1
ATD1
Bit 0
PTB0
ATD0
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.
ATD[7:0] — ADC Channels
PTB7/ATD7–PTB0/ATD0 are eight of the ADC channels. The ADC channel select bits, CH[4:0],
determine whether the PTB7/ATD7–PTB0/ATD0 pins are ADC channels or general-purpose I/O pins.
If an ADC channel is selected and a read of this corresponding bit in the port B data register occurs,
the data will be 0 if the data direction for this bit is programmed as an input. Otherwise, the data will
reflect the value in the data latch. See Chapter 3 Analog-to-Digital Converter (ADC).
Data direction register B (DDRB) does not affect the data direction of port B pins that are being used
by the ADC. However, the DDRB bits always determine whether reading port B returns to the states
of the latches or a 0.
13.3.2 Data Direction Register B
Data direction register B 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.
Address: $0005
Bit 7
6
5
4
3
2
1
Read:
DDRB7
Write:
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
Reset: 0
0
0
0
0
0
0
Figure 13-5. Data Direction Register B (DDRB)
Bit 0
DDRB0
0
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
MC68HC908AS32A Data Sheet, Rev. 2.0
Freescale Semiconductor
153