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| 型號： | PIC12F509-I/MS |
| 廠商： | Microchip Technology |
| 文件頁數(shù)： | 27/44頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC PIC MCU FLASH 1KX12 8MSOP |
| 產(chǎn)品培訓(xùn)模塊： | Asynchronous Stimulus 8-bit PIC® Microcontroller Portfolio |
| 標(biāo)準(zhǔn)包裝： | 100 |
| 系列： | PIC® 12F |
| 核心處理器： | PIC |
| 芯體尺寸： | 8-位 |
| 速度： | 4MHz |
| 外圍設(shè)備： | POR，WDT |
| 輸入/輸出數(shù)： | 5 |
| 程序存儲器容量： | 1.5KB（1K x 12） |
| 程序存儲器類型： | 閃存 |
| RAM 容量： | 41 x 8 |
| 電壓 - 電源 (Vcc/Vdd)： | 2 V ~ 5.5 V |
| 振蕩器型： | 內(nèi)部 |
| 工作溫度： | -40°C ~ 85°C |
| 封裝/外殼： | 8-TSSOP，8-MSOP（0.118"，3.00mm 寬） |
| 包裝： | 管件 |
| 產(chǎn)品目錄頁面： | 637 (CN2011-ZH PDF) |
| 配用： | AC162059-ND - HEADER INTRFC MPLAB ICD2 8/14PIN AC164325-ND - MODULE SKT FOR 8MSOP DVA12XP080-ND - ADAPTER DEVICE FOR MPLAB-ICE |
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2009 Microchip Technology Inc.
DS41236E-page 33
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 pres-
ent 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
;
PORTB latch
PORTB pins
;
----------
BCF
PORTB, 5 ;--01 -ppp
--11 pppp
BCF
PORTB, 4 ;--10 -ppp
--11 pppp
MOVLW
007h;
TRIS
PORTB
;--10 -ppp
--11 pppp
;
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).
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
This example shows a write to PORTB
followed by a read from PORTB.
Data setup time = (0.25 TCY – TPD)
where: TCY = instruction cycle
TPD = propagation delay
Therefore, at higher clock frequencies, a
write followed by a read may be problematic.
(Read PORTB)
Port pin
written here
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