Datasheet

28
BIG8051
MikroElektronika
page
Pull-up/pull-down resistors enable you to set the logic level on all microcontroller’s input pins when they are in idle state.
This level depends on the position of the pull-up/pull-down jumper. The RP7.0 pin with the relevant DIP switch SW8,
jumper J8 and P7.0 push button with jumper J10 are used here for the purpose of explaining the performance of pull-up/
pull-down resistors. The principle of their operation is the same for all other microcontroller pins.
In order to enable the PORT7 port pins to
be connected to pull-down resistors, it is
necessary to place jumper J8 in the Down
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pin to be supplied with a logic zero (0V) in
idle state over jumper J8 and 8x10k resistor
network. To provide the P7.0 pin with this
signal, it is necessary to set switch P7.0 on
the DIP switch SW8 to the ON position.
As a result, every time you press the P7.0
push button, the P7.0 pin will be fed with
a logic one (VCC-3.3 voltage), provided
that jumper J10 is placed in the VCC-3.3
position.
In order to enable port PORT7 pins to be
connected to pull-up resistors and the port
input pins to be supplied with a logic zero
(0), it is necessary to place jumper J8 in
the Up position and jumper J10 in the GND
position. This enables any port PORT7
input pin, when it is in idle state, to be
driven high (3.3V) over the 10k resistor.
As a result, every time you press the P7.0
push button, the P7.0 pin will be fed with a
logic zero (0V), provided that switch P7.0
on the DIP switch SW8 is set to the ON
position.
In case that jumpers J8 and J10 are in the
same positions, pressure on any button will
not cause input pins to change their logic
state.
Figure 21-5: Jumper J8 in pull-down and jumper J10 in pull-up position
)LJXUH Jumper J8 in pull-up and jumper J10 in pull-down position
)LJXUH Jumpers J8 and J10 in the same positions