參數(shù)資料
型號(hào)： PIC12F505
廠商： Microchip Technology Inc.
元件分類： 8位微控制器
英文描述： 8/14-Pin, 8-Bit Flash Microcontrollers
中文描述： 8/14-Pin，8位閃存微控制器
文件頁(yè)數(shù)： 33/100頁(yè)
文件大?。?/td> 741K
代理商： PIC12F505
2007 Microchip Technology Inc.
Preliminary
DS41236C-page 31
PIC12F508/509/16F505
5.5
I/O Programming Considerations
5.5.1
BIDIRECTIONAL I/O PORTS
Some instructions operate internally as read followed
by write operations. The
BCF
and
BSF
instructions, for
example, read the entire port into the CPU, execute the
bit operation and re-write the result. Caution must be
used when these instructions are applied to a port
where one or more pins are used as input/outputs. For
example, a
BSF
operation on bit 5 of PORTB/GPIO will
cause all eight bits of PORTB/GPIO to be read into the
CPU, bit 5 to be set and the PORTB/GPIO value to be
written to the output latches. If another bit of PORTB/
GPIO is used as a bidirectional I/O pin (say bit
0
) and it
is defined as an input at this time, the input signal
present on the pin itself would be read into the CPU and
rewritten to the data latch of this particular pin, overwrit-
ing the previous content. As long as the pin stays in the
Input mode, no problem occurs. However, if bit
0
is
switched into Output mode later on, the content of the
data latch may now be unknown.
Example 5-1 shows the effect of two sequential
Read-Modify-Write instructions (e.g.,
BCF, BSF
, etc.)
on an I/O port.
A pin actively outputting a high or a low should not be
driven from external devices at the same time in order
to change the level on this pin (“wired OR”, “wired
AND”). The resulting high output currents may damage
the chip.
EXAMPLE 5-1:
READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT(e.g. PIC16F505)
5.5.2
SUCCESSIVE OPERATIONS ON
I/O PORTS
The actual write to an I/O port happens at the end of an
instruction cycle, whereas for reading, the data must be
valid at the beginning of the instruction cycle (Figure 5-2).
Therefore, care must be exercised if a write followed by
a read operation is carried out on the same I/O port. The
sequence of instructions should allow the pin voltage to
stabilize (load dependent) before the next instruction
causes that file to be read into the CPU. Otherwise, the
previous state of that pin may be read into the CPU rather
than the new state. When in doubt, it is better to separate
these instructions with a
NOP
or another instruction not
accessing this I/O port.
FIGURE 5-2:
SUCCESSIVE I/O OPERATION (PIC16F505 Shown)
;Initial PORTB Settings
;PORTB<5:3> Inputs
;PORTB<2:0> Outputs
;
;
;
BCF
PORTB, 5 ;--01 -ppp
BCF
PORTB, 4 ;--10 -ppp
MOVLW
007h;
TRIS
PORTB
;
Note
1:
The user may have expected the pin values to
be ‘
--00 pppp
’. The 2nd
BCF
caused RB5 to
be latched as the pin value (High).
PORTB latch
----------
PORTB pins
----------
--11 pppp
--11 pppp
;--10 -ppp
--11 pppp
PC
PC + 1
PC + 2
PC + 3
Q1 Q2
Q3 Q4
Q1 Q2
Q3 Q4
Q1
Q2 Q3 Q4
Q1 Q2
Q3 Q4
Instruction
Fetched
RB<5:0>
MOVWF
PORTB
NOP
Port pin
sampled here
NOP
MOVF
PORTB
,
W
Instruction
Executed
MOVWF PORTB
(Write to PORTB)
NOP
MOVF PORTB,W
(Read PORTB)
This example shows a write to PORTB
followed by a read from PORTB.
Data setup time = (0.25 T
CY
– T
PD
)
where: T
CY
= instruction cycle.
T
PD
= propagation delay
Therefore, at higher clock frequencies, a
write followed by a read may be problematic.
Port pin
written here
相關(guān)PDF資料
PDF描述
PIC12F506 8/14-Pin, 8-Bit Flash Microcontroller
PIC12F510_07 8/14-Pin, 8-Bit Flash Microcontroller
PIC12F510 8/14-Pin, 8-Bit Flash Microcontroller
PIC12F519 8-Pin, 8-Bit Flash Microcontroller
PIC12F609 8-bit PIC㈢ Microcontrollers with High Voltage Support and Fan Control Capabilities
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
PIC12F505TE/MC 制造商:MICROCHIP 制造商全稱:Microchip Technology 功能描述:8/14-Pin, 8-Bit Flash Microcontrollers
PIC12F505TE/MG 制造商:MICROCHIP 制造商全稱:Microchip Technology 功能描述:8/14-Pin, 8-Bit Flash Microcontrollers
PIC12F505TE/MS 制造商:MICROCHIP 制造商全稱:Microchip Technology 功能描述:8/14-Pin, 8-Bit Flash Microcontrollers
PIC12F505TE/P 制造商:MICROCHIP 制造商全稱:Microchip Technology 功能描述:8/14-Pin, 8-Bit Flash Microcontrollers
PIC12F505TE/SL 制造商:MICROCHIP 制造商全稱:Microchip Technology 功能描述:8/14-Pin, 8-Bit Flash Microcontrollers
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。

采購(gòu)需求

(若只采購(gòu)一條型號(hào)，填寫(xiě)一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

*型號(hào) *數(shù)量 廠商 批號(hào) 封裝
添加更多采購(gòu)

我的聯(lián)系方式

*
*
*