Port B; Port B Data Register (Ptb) - Motorola MC68HC908AB32 Technical Data Manual

Input/Output (I/O) Ports

17.4 Port B

17.4.1 Port B Data Register (PTB)

Alternative Function:
NOTE:
Technical Data
318
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
The port B data register contains a data latch for each of the eight port B
pins.
Address: $0001
Bit 7 6
Read:
PTB7 PTB6
Write:
Reset:
ATD7 ATD6
Figure 17-5. Port B Data Register (PTB)
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.
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.
Input/Output (I/O) Ports
(ADC)).
5 4 3
PTB5 PTB4 PTB3
Unaffected by reset
ATD5 ATD4 ATD3
Section 14.
2 1 Bit 0
PTB2 PTB1 PTB0
ATD2 ATD2 ATD0
MC68HC908AB32 Rev. 1.0
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MOTOROLA