MC908AZ32ACFUE Datasheet, PDF (246/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

I/O Ports
23.3 Port B
Port B is an 8-bit special function port that shares all of its pins with the analog-to-digital converter.
23.3.1 Port B Data Register
The port B data register contains a data latch for each of the eight port B pins.
Address:
Read:
Write:
Reset:
Alternate
Functions:
$0001
Bit 7
PTB7
ATD7
6
5
4
3
2
PTB6
PTB5
PTB4
PTB3
PTB2
Unaffected by Reset
ATD6
ATD5
ATD4
ATD3
ATD2
Figure 23-5. 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–PTB0 are eight of the analog-to-digital converter channels. The ADC channel select bits,
CH[4:0], determine whether the PTB7–PTB0 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 21 Analog-To-Digital Converter (ADC-15)). 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 logic 0.
23.3.2 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.
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 23-6. 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
MC68HC908AZ32A Data Sheet, Rev. 2
246
Freescale Semiconductor