ST72T311 ST Microelectronics, ST72T311 Datasheet - Page 27

• Manufacturer Part Number: ST72T311
• Description: 8-BIT MCU WITH 8 TO 16K OTP/EPROM
• Manufacturer: ST Microelectronics

I/O PORTS (Cont’d)
4.1.2.4 Analog Alternate Function
When the pin is used as an ADC input the I/O must
be configured as input, floating. The analog multi-
plexer (controlled by the ADC registers) switches
the analog voltage present on the selected pin to
the common analog rail which is connected 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 Maximum
Ratings.
Figure 20. Recommended I/O State Transition Diagram
with interrupt
INPUT
no interrupt
INPUT
4.1.3 I/O Port Implementation
The hardware implementation on each I/O port de-
pends on the settings in the DDR and OR registers
and specific feature of the I/O port such as ADC In-
put (see Figure 21) or true open drain. Switching
these I/O ports from one state to another should
be done in a sequence that prevents unwanted
side effects. Recommended safe transitions are il-
lustrated in Figure 20. Other transitions are poten-
tially risky and should be avoided, since they are
likely to present unwanted side-effects such as
spurious interrupt generation.
open-drain
OUTPUT
ST72E311 ST72T311
OUTPUT
push-pull
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