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ST7LITEUS2, ST7LITEUS5
I/O ports
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9.2.3 Alternate
functions
When an on-chip peripheral is configured to use a pin, the alternate function is automatically
selected. This alternate function takes priority over the standard I/O programming under the
following conditions:
●
When the signal is coming from an on-chip peripheral, the I/O pin is automatically
configured in output mode (push-pull or open drain according to the peripheral).
●
When the signal is going to an on-chip peripheral, the I/O pin must be configured in
floating input mode. In this case, the pin state is also digitally readable by addressing
the DR register.
Note:
1
Input pull-up configuration can cause unexpected value at the input of the alternate
peripheral input.
2
When an on-chip peripheral use a pin as input and output, this pin has to be configured in
input floating mode.
Figure 28.
I/O port general block diagram
DR
DDR
OR
DATA BU
S
PAD
V
DD
ALTERNATE
ENABLE
ALTERNATE
OUTPUT
1
0
OR SEL
DDR SEL
DR SEL
PULL-UP
CONDITION
P-BUFFER
(see table below)
N-BUFFER
PULL-UP
(see table below)
1
0
ANALOG
INPUT
If implemented
ALTERNATE
INPUT
V
DD
DIODES
(see table below)
FROM
OTHER
BITS
EXTERNAL
SOURCE (ei
x
)
INTERRUPT
POLARITY
SELECTION
CMOS
SCHMITT
TRIGGER
REGISTER
ACCESS
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