ST7265XEVALMS STMicroelectronics, ST7265XEVALMS Datasheet - Page 47

• Manufacturer Part Number: ST7265XEVALMS
• Manufacturer: STMicroelectronics

Specifications of ST7265XEVALMS

• Lead Free Status / Rohs Status: Supplier Unconfirmed

I/O PORTS (Cont’d)
9.2.2 Output Modes
Two different output modes can be selected by
software through the OR register: Output push-pull
and open-drain.
DR register value and output pin status:
The output configuration is selected by setting the
corresponding DDR register bit. In this case, writ-
ing the DR register applies this digital value to the
I/O pin through the latch. Reading the DR register
returns the digital value present on the external I/O
pin. Consequently even in output mode a value
written to an open drain port may differ from the
value read from the port. For example, if software
writes a ‘1’ in the latch, this value will be applied to
the pin, but the pin may stay at ‘0’ depending on
the state of the external circuitry. For this reason,
bit manipulation even using instructions like BRES
and BSET must not be used on open drain ports
as they work by reading a byte, changing a bit and
writing back a byte. A workaround for applications
requiring bit manipulation on Open Drain I/Os is
given in
9.2.3 Alternate Functions
When an on-chip peripheral is configured to use a
pin, the alternate function is automatically select-
ed. This alternate function takes priority over the
standard I/O programming.
When the signal comes from an on-chip peripher-
al, the I/O pin is automatically configured in output
mode (push-pull or open drain according to the pe-
ripheral).
When the signal goes to an on-chip peripheral, the
I/O pin must be configured in input mode. In this
DR
0
1
Section
Push-pull
9.2.5.
V
V
DD
SS
Open-drain
Floating
Vss
case, the pin state is also digitally readable by ad-
dressing the DR register.
Note: Input pull-up configuration can cause unex-
pected values at the input of the alternate periph-
eral input. When an on-chip peripheral uses a pin
as input and output, this pin has to be configured
in input floating mode.
CAUTION: The alternate function must not be ac-
tivated as long as the pin is configured as input
with interrupt, in order to avoid generating spurious
interrupts.
Analog alternate function
When the pin is used as an ADC input, the I/O
must be configured as floating input. The analog
multiplexer (controlled by the ADC registers)
switches the analog voltage present on the select-
ed pin to the common analog rail which is connect-
ed to the ADC input.
It is recommended not to change the voltage level
or loading on any port pin while conversion is in
progress. Furthermore it is recommended not to
have clocking pins located close to a selected an-
alog pin.
WARNING: The analog input voltage level must
be within the limits stated in the absolute maxi-
mum ratings.
9.2.4 V
The microcontroller is able to power the I/O pins
from a specific supply rail connected to the V
pin.
If V
be used and are tied to ground. Furthermore, this
is also true in an application where the internal
regulator is used but not yet enabled (this is at
least the case during the reset stage).
DDF
DDF
is not present, all V
-Powered I/Os
DDF
-driven I/Os cannot
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DDF
1