參數(shù)資料
型號(hào): HMS81C20XXA
廠商: Electronic Theatre Controls, Inc.
英文描述: CMOS Single-Chip 8-Bit Microcontroller with A/D Converter & VFD Driver
中文描述: CMOS單芯片8位微控制器與A / D轉(zhuǎn)換器
文件頁(yè)數(shù): 85/107頁(yè)
文件大?。?/td> 1482K
代理商: HMS81C20XXA
HMS81C2012A/2020A
SEP. 2004 Ver 2.00
81
than the power voltage level (by approximately 0.3V), a cur-
rent begins to flow. Therefore, if cutting off the output tran-
sistor at an I/O port puts the pin signal into the high-
impedance state, a current flow across the ports input tran-
sistor, requiring it to fix the level by pull-up or other means.
It should be set properly in order that current flow through
port doesn't exist.
First conseider the setting to input mode. Be sure that there
is no current flow after considering its relationship with
external circuit. In input mode, the pin impedance viewing
from external MCU is very high that the current doesn’t
flow.
But input voltage level should be V
SS
or V
DD
. Be careful
that if unspecified voltage, i.e. if unfirmed voltage level
(not V
SS
or V
DD
) is applied to input pin, there can be little
current (max. 1mA at around 2V) flow.
If it is not appropriate to set as an input mode, then set to
output mode considering there is no current flow. Setting
to High or Low is decided considering its relationship with
external circuit. For example, if there is external pull-up re-
sistor then it is set to output mode, i.e. to High, and if there
is external pull-down register, it is set to low.
Figure 17-7 Application Example of Unused Input Port
Figure 17-8 Application Example of Unused Output Port
INPUT PIN
V
DD
GND
i
V
DD
X
Weak pull-up current flows
V
DD
internal
pull-up
INPUT PIN
i
V
DD
X
Very weak current flows
V
DD
O
O
OPEN
OPEN
i=0
O
i=0
O
GND
When port is configured as an input, input level should
be closed to 0V or 5V to avoid power consumption.
OUTPUT PIN
GND
i
In the left case, much current flows from port to GND.
X
ON
OFF
OUTPUT PIN
GND
i
In the left case, Tr. base current flows from port to GND.
To avoid power consumption, there should be low output
to the port .
i=0
X
OFF
ON
V
DD
L
ON
OFF
OPEN
GND
V
DD
L
ON
OFF
ON
OFF
O
O
V
DD
O
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