MC68HC908GR8 Datasheet, PDF (148/286 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Input/Output Ports (I/O)
Address: $000D
Bit 7
6
5
4
3
2
1
Bit 0
Read: 0
0
0
0
PTAPUE3 PTAPUE2 PTAPUE1 PTAPUE0
Write:
Reset: 0
0
0
0
0
0
0
0
= Unimplemented
Figure 16-5. Port A Input Pullup Enable Register (PTAPUE)
PTAPUE3–PTAPUE0 — Port A Input Pullup Enable Bits
These writeable bits are software programmable to enable pullup devices on an input port bit.
1 = Corresponding port A pin configured to have internal pullup
0 = Corresponding port A pin has internal pullup disconnected
16.3 Port B
Port B is a 6-bit special-function port that shares all six of its pins with the analog-to-digital converter
(ADC) module.
16.3.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the six port pins.
Address: $0001
Bit 7
6
5
4
3
2
1
Bit 0
Read: 0
Write:
0
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Reset:
Unaffected by reset
Alternative Function:
AD5
AD4
AD3
AD2
AD1
AD0
= Unimplemented
Figure 16-6. Port B Data Register (PTB)
PTB5–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.
AD5–AD0 — Analog-to-Digital Input Bits
AD5–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.
NOTE
Care must be taken when reading port B while applying analog voltages to
AD5–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.
PTB4 and 5 are not available in a 28-pin DIP and SOIC package
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
148
Freescale Semiconductor