GMS81C2012/GMS81C2020
HYUNDAI MicroElectronics
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.
But input voltage level should be VSS or VDD. Be careful
that if unspecified voltage, i.e. if unfirmed voltage level
(not VSSor VDD) 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.
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.
VDD
INPUT PIN
INPUT PIN
VDD
VDD
VDD
internal
pull-up
i=0
OPEN
O
i
O
i
Very weak current flows
VDD
GND
i=0
X
GND
X
OPEN
O
Weak pull-up current flows
O
When port is configured as an input, input level should
be closed to 0V or 5V to avoid power consumption.
Figure 17-7 Application Example of Unused Input Port
OUTPUT PIN
OUTPUT PIN
ON
VDD
ON
VDD
OPEN
L
L
OFF
ON
OFF
ON
O
i=0
OFF
OFF
i
i
VDD
GND
GND
GND
ON
X
O
X
OFF
In the left case, Tr. base current flows from port to GND.
To avoid power consumption, there should be low output
to the port .
O
In the left case, much current flows from port to GND.
Figure 17-8 Application Example of Unused Output Port
84
MAR. 2000 Ver 1.00
HYNIX [ HYNIX SEMICONDUCTOR ]
