MC68HC08AS20 Datasheet, PDF (183/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

15.4 Port B
Port B is an 8-bit special function port that shares all of its pins with the
analog-to-digital converter (ADC).
15.4.1 Port B Data Register
The port B data register contains a data latch for each of the eight port
B pins.
Address: $0001
Bit 7
6
5
4
3
2
1
Read:
PTB7
Write:
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
Reset:
Unaffected by Reset
Alternate
Functions:
ATD7
ATD6
ATD5
ATD4
ATD3
ATD2
ATD1
Figure 15-4. Port B Data Register (PTB)
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/ATD7–PTB0/ATD0 are eight of the 15 analog-to-digital
converter channels. The ADC channel select bits, CH[4:0], determine
whether the PTB7/ATD7–PTB0/ATD0 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
Section 19. Analog-to-Digital Converter (ADC).) 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.
MC68HC08AS20 — Rev. 4.1
Freescale Semiconductor
Advance Information
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