MC68HC908GZ8 Datasheet, PDF (205/344 Pages) Motorola, Inc – Microcontrollers

Input/Output (I/O) Ports
Port B
NOTE:
AD7–AD0 — Analog-to-Digital Input Bits
AD7–AD0 are pins used for the input channels to the analog-to-digital converter
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.
Care must be taken when reading port B while applying analog voltages to
AD7–AD0 pins. If the appropriate ADC channel is not enabled, excessive current
drain may occur if analog voltages are applied to the PTBx/ADx pin, while PTB is
read as a digital input. Those ports not selected as analog input channels are
considered digital I/O ports.
17.3.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or
an output. Writing a 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 17-7. Data Direction Register B (DDRB)
Bit 0
DDRB0
0
NOTE:
DDRB7–DDRB0 — Data Direction Register B Bits
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
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.
Figure 17-8 shows the port B I/O logic.
MC68HC908GZ8
Freescale Semiconductor
Input/Output (I/O) Ports
Data Sheet
205