GMS81C5108
Minimizing Current Consumption
It should be set properly that current flow through port
doesn't exist.
The Stop mode is designed to reduce power consumption.
To minimize current drawn during Stop mode, the user
should turn-off output drivers that are sourcing or sinking
current, if it is practical.
First consider 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.
Note: In the STOP operation, the power dissipation asso-
ciated with the oscillator and the internal hardware is low-
ered; however, the power dissipation associated with the
pin interface (depending on the external circuitry and pro-
gram) is not directly determined by the hardware operation
of the STOP feature. This point should be little current flows
when the input level is stable at the power voltage level
(VDD/VSS); however, when the input level becomes higher
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-saving register, it is set to low.
V
DD
INPUT PIN
INPUT PIN
V
DD
V
DD
internal
pull-up
i=0
i=0
V
DD
OPEN
O
O
i
O
i
Very weak current flows
V
DD
GND
GND
X
X
OPEN
Weak pull-up current flows
When port is configured as an input, input level should
O
be closed to 0V or V to avoid power consumption.
DD
Figure 10-10 Application Example of Unused Input Port
OUTPUT PIN
OUTPUT PIN
ON
V
ON
DD
V
DD
OPEN
L
L
OFF
ON
OFF
ON
O
i=0
OFF
OFF
i
i
V
DD
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 10-11 Application Example of Unused Output Port
42
JUNE 2001 Ver 1.0
HYNIX [ HYNIX SEMICONDUCTOR ]
