MC68HC908GZ8 FREESCALE [Freescale Semiconductor, Inc], MC68HC908GZ8 Datasheet - Page 160

• Manufacturer Part Number: MC68HC908GZ8
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Input/Output (I/O) Ports
PTAPUE7–PTAPUE0 — Port A Input Pullup Enable Bits
13.4 Port B
Port B is an 8-bit special-function port that shares all eight of its pins with the analog-to-digital converter
(ADC) module.
13.4.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the eight port pins.
PTB7–PTB0 — Port B Data Bits
AD7–AD0 — Analog-to-Digital Input Bits
13.4.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or an output. Writing a
logic 1 to a DDRB bit enables the output buffer for the corresponding port B pin; a logic 0 disables the
output buffer.
160
These writable bits are software programmable to enable pullup devices on an input port bit.
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 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.
See
1 = Corresponding port A pin configured to have internal pullup
0 = Corresponding port A pin has internal pullup disconnected
Chapter 3 Analog-to-Digital Converter (ADC)
Alternative
Function:
Address:
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.
Reset:
Read:
Write:
$0001
PTB7
Bit 7
AD7
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Figure 13-6. Port B Data Register (PTB)
PTB6
AD6
6
PTB5
AD5
5
NOTE
Unaffected by reset
PTB4
AD4
4
for more information.
PTB3
AD3
3
PTB2
AD2
2
PTB1
AD1
1
Freescale Semiconductor
PTB0
Bit 0
AD0