MC68HC908GR8A_07 Datasheet, PDF (120/260 Pages) Freescale Semiconductor, Inc – Microcontrollers

Input/Output (I/O) Ports
12.3 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.
12.3.1 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 12-6. 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 PTB5 are not available in 28-pin DIP and SOIC packages.
12.3.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or an output. Writing a 1
to a DDRB bit enables the output buffer for the corresponding port B pin; a 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0005
Bit 7
0
0
6
5
0
DDRB5
0
0
= Unimplemented
4
DDRB4
0
3
DDRB3
0
2
DDRB2
0
1
DDRB1
0
Bit 0
DDRB0
0
Figure 12-7. Data Direction Register B (DDRB)
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
120
Freescale Semiconductor