參數(shù)資料
型號： MC68HC05J5P
廠商： MOTOROLA INC
元件分類： 微控制器/微處理器
英文描述： 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDIP20
封裝： PLASTIC, DIP-20
文件頁數(shù)： 41/69頁
文件大?。?/td> 394K
代理商： MC68HC05J5P
GENERAL RELEASE SPECIFICATION
December 11, 1996
MOTOROLA
INPUT/OUTPUT PORTS
MC68HC05J5
7-6
REV 1.1
7.3.3 Port B Pull-down/up Register
All Port B I/O pins may have software programmable pull-down/up devices
enabled by a mask option. If the pull-down/up mask option is selected, the pull-
down/up is activated whenever the corresponding bit in the PDURB is clear. A
pull-down on an I/O pin is activated only if the I/O pin is programmed as an input
whereas a Pull-up device on an I/O pin is always activated whenever enabled,
regardless of port direction.
The PDURB is a write-only register. Any reads of location $0011 will return unde-
ned results. Since reset clears both the DDRB and the PDURB, all pins will ini-
tialize as inputs with the pull-down devices active and pull-up devices active (if
chosen via mask option).
Typical value of port B pull-up is 100K
.
7.4
I/O PORT PROGRAMMING
All I/O pins can be programmed as inputs or outputs, with or without pull-down/up
devices.
7.4.1 Pin Data Direction
The direction of a pin is determined by the state of its corresponding bit in the
associated port Data Direction Register (DDR). A pin is congured as an output if
its corresponding DDR bit is set to a logic one. A pin is congured as an input if its
corresponding DDR bit is cleared to a logic zero.
The data direction bits DDRB0 to DDRB2 and DDRA0 to DDRA7 are read/write
bits which can be manipulated with read-modify-write instructions. At power-on or
reset, all DDRs are cleared which congures all port pins as inputs. If the pull-
down/up mask option is chosen, all pins will initially power-up with their software
programmable pull-downs/ups enabled.
7.4.2 Output Pin
When an I/O pin is programmed as an output pin, the state of the corresponding
data register bit will determine the state of the pin. The state of the data register
bits can be altered by writing to address $0000 for Port A and address $0001 for
Port B. Reads of the corresponding data register bit at address $0000 or $0001
will return the state of the data register bit (not the state of the I/O pin itself).
Therefore bit manipulation is possible on all pins programmed as outputs.
If the corresponding bit in the pull-down/up register is clear (and the pull-down/up
mask option is chosen), only output pins with pull-ups have an activated pull-up
device connected to the pin. For those pins with pull-downs and congured as out-
put pins, the pull-downs will be inactivated regardless of the state of the corre-
sponding pull-down/up register bit. Since the pull-down/up register bits are write-
only, bit manipulation should not be used on these register bits.
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