GMS81C2112 Datasheet, PDF (84/107 Pages) Hynix Semiconductor – HYNIX SEMICONDUCTOR 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C2112/GMS81C2120
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_SSor 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.
INPUT PIN
V_DD
V_DD
internal
pull-up
i
GND
V_DD
X
Weak pull-up current flows
V_DD
O
OPEN
O
INPUT PIN
OPEN
i
V_DD
i=0
O
Very weak current flows
X
i=0
GND
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
ON
OFF _i
GND
X
ON
OPEN
OFF
O
V_DD
ON
O ^OFF
In the left case, much current flows from port to GND.
OUTPUT PIN
ON
OFF _i
V_DD
L
GND
OFF
V_DD
L
ON i=0
GND
X
O
In the left case, Tr. base current flows from port to GND.
To avoid power consumption, there should be low output
to the port .
Figure 17-8 Application Example of Unused Output Port
78
JUNE. 2001 Ver 1.00