GMS81C5108 Datasheet, PDF (45/102 Pages) Hynix Semiconductor – HYNIX SEMICONDUCTOR INC. 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C5108
Minimizing Current Consumption
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.
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
(V_DD/V_SS); 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.
It should be set properly that current flow through port
doesn't exist.
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.
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-saving 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
V_DD
OPEN
i
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 V_DD to avoid power consumption.
Figure 10-10 Application Example of Unused Input Port
OUTPUT PIN
ON
OFF _i
GND
X
ON
OPEN
OFF
O
V_DD
ON
OFF
O
In the left case, much current flows from port to GND.
OUTPUT PIN
ON
V_DD
L
OFF
V_DD
L
OFF _i
GND
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 10-11 Application Example of Unused Output Port
42
JUNE 2001 Ver 1.0