Port B; Port B Data Register - Motorola MC68HC908GP32 Technical Data Manual

16.4 Port B

16.4.1 Port B Data Register

NOTE:
MC68HC908GP32 MC68HC08GP32
•
MOTOROLA
Freescale Semiconductor, Inc.
Port B is an 8-bit special-function port that shares all eight of its pins with
the analog-to-digital converter (ADC) module.
The port B data register (PTB) contains a data latch for each of the eight
port pins.
Address: $0001
Bit 7 6
Read:
PTB7 PTB6
Write:
Reset:
Alternate
AD7 AD6
Function:
Figure 16-6. Port B Data Register (PTB)
PTB7–PTB0 — 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.
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.
Rev. 6
—
Input/Output (I/O) Ports
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5 4 3
PTB5 PTB4 PTB3
Unaffected by reset
AD5 AD4 AD3
Input/Output (I/O) Ports
Port B
2 1 Bit 0
PTB2 PTB1 PTB0
AD2 AD1 AD0
Technical Data
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