ST72F63 STMICROELECTRONICS [STMicroelectronics], ST72F63 Datasheet - Page 25

• Manufacturer Part Number: ST72F63
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

9 I/O PORTS
9.1 Introduction
The I/O ports offer different functional modes:
– Transfer of data through digital inputs and out-
– Analog signal input (ADC)
– Alternate signal input/output for the on-chip pe-
– External interrupt generation
An I/O port consists of up to 8 pins. Each pin can
be programmed independently as a digital input
(with or without interrupt generation) or a digital
output.
9.2 Functional description
Each port is associated to 2 main registers:
– Data Register (DR)
– Data Direction Register (DDR)
Each I/O pin may be programmed using the corre-
sponding register bits in DDR register: bit X corre-
sponding to pin X of the port. The same corre-
spondence is used for the DR register.
Table 8. I/O Pin Functions
Input Modes
The input configuration is selected by clearing the
corresponding DDR register bit.
In this case, reading the DR register returns the
digital value applied to the external I/O pin.
Note 1: All the inputs are triggered by a Schmitt
trigger.
Note 2: When switching from input mode to output
mode, the DR register should be written first to
output the correct value as soon as the port is con-
figured as an output.
Interrupt function
When an I/O is configured as an Input with Inter-
rupt, an event on this I/O can generate an external
Interrupt request to the CPU. The interrupt sensi-
puts and for specific pins
ripherals
DDR
0
1
MODE
Output
Input
tivity is given independently according to the de-
scription mentioned in the ITRFRE interrupt regis-
ter.
Each pin can independently generate an Interrupt
request.
Each external interrupt vector is linked to a dedi-
cated group of I/O port pins (see Interrupts sec-
tion). If more than one input pin is selected simul-
taneously as an interrupt source, this is logically
ORed. For this reason if one of the interrupt pins is
tied low, the other ones are masked.
Output Mode
The pin is configured in output mode by setting the
corresponding DDR register bit (see Table 7).
In this mode, writing “0” or “1” to the DR register
applies this digital value to the I/O pin through the
latch. Therefore, the previously saved value is re-
stored when the DR register is read.
Note: The interrupt function is disabled in this
mode.
Digital Alternate Function
When an on-chip peripheral is configured to use a
pin, the alternate function is automatically select-
ed. This alternate function takes priority over
standard I/O programming. 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 has to be configured in input mode. In
this case, the pin’s state is also digitally readable
by addressing the DR register.
Notes:
1. Input pull-up configuration can cause an unex-
pected value at the input of the alternate peripher-
al input.
2. When the on-chip peripheral uses a pin as input
and output, this pin must be configured as an input
(DDR = 0).
Warning : The alternate function must not be acti-
vated as long as the pin is configured as an input
with interrupt in order to avoid generating spurious
interrupts.
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