Input/Output (I/O) Ports
Technical Data
MC68HC908AB32
—
Rev. 1.0
318
Input/Output (I/O) Ports
MOTOROLA
17.4 Port B
Port B is an 8-bit special function port that shares all eight of its port pins
with the analog-to-digital converter (ADC) module (see
Analog-to-Digital Converter (ADC)
17.4.1 Port B Data Register (PTB)
The port B data register contains a data latch for each of the eight port B
pins.
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
ATD[7:0] 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.
NOTE:
Care must be taken when reading port B while applying analog voltages
to ATD[7:0] pins. If the appropriate ADC channel is not enabled,
excessive current drain may occur if analog voltages are applied to the
PTBx/ATDx pin, while PTB is read as a digital input. Those ports not
selected as analog input channels are considered digital I/O ports.
Address:
$0001
Bit 7
6
5
4
3
2
1
Bit 0
Read:
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Write:
Reset:
Unaffected by reset
Alternative Function:
ATD7
ATD6
ATD5
ATD4
ATD3
ATD2
ATD2
ATD0
Figure 17-5. Port B Data Register (PTB)
Summary of Contents for MC68HC908AB32
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