Specifications

ST72104Gx, ST72215Gx, ST72216Gx, ST72254Gx
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I/O PORTS (Cont’d)
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.
9.3 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 or true open drain.
Switching these I/O ports from one state to anoth-
er should be done in a sequence that prevents un-
wanted side effects. Recommended safe transi-
tions are illustrated in Figure 2. Other transitions
are potentially risky and should be avoided, since
they are likely to present unwanted side-effects
such as spurious interrupt generation.
Figure 22. Interrupt I/O Port State Transitions
The I/O port register configurations are summa-
rized as follows.
Interrupt Ports
PA7, PA5, PA3:0, PB7:0, PC5:0 (with pull-up)
True Open Drain Interrupt Ports
PA6, PA4 (without pull-up)
Table 8. Port Configuration
MODE DDR OR
floating input 0 0
pull-up interrupt input 0 1
open drain output 1 0
push-pull output 1 1
MODE DDR OR
floating input 0 0
floating interrupt input 0 1
open drain (high sink ports) 1 X
01
floating/pull-up
interrupt
INPUT
00
floating
(reset state)
INPUT
10
open-drain
OUTPUT
11
push-pull
OUTPUT
XX
= DDR, OR
Port Pin name
Input (DDR = 0) Output (DDR = 1)
OR = 0 OR = 1 OR = 0 OR = 1 High-Sink
Port A
PA7 floating pull-up interrupt open drain push-pull
Yes
PA6 floating floating interrupt true open-drain
PA5 floating pull-up interrupt open drain push-pull
PA4 floating floating interrupt true open-drain
PA3:0 floating pull-up interrupt open drain push-pull
Port B PB7:0 floating pull-up interrupt open drain push-pull
No
Port C PC7:0 floating pull-up interrupt open drain push-pull