ST72521 STMICROELECTRONICS [STMicroelectronics], ST72521 Datasheet - Page 50

• Manufacturer Part Number: ST72521
• Description: 8-BIT MCU WITH NESTED INTERRUPTS, FLASH, 10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C, CAN INTERFACE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72521
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
are potentially risky and should be avoided, since
they are likely to present unwanted side-effects
such as spurious interrupt generation.
50/211
Figure 31
Other transitions
Figure 31. Interrupt I/O Port State Transitions
9.4 LOW POWER MODES
9.5 INTERRUPTS
The external interrupt event generates an interrupt
if the corresponding configuration is selected with
DDR and OR registers and the interrupt mask in
the CC register is not active (RIM instruction).
floating/pull-up
WAIT
HALT
External interrupt on
selected external
event
Mode
Interrupt Event
interrupt
INPUT
01
No effect on I/O ports. External interrupts
cause the device to exit from WAIT mode.
No effect on I/O ports. External interrupts
cause the device to exit from HALT mode.
(reset state)
floating
INPUT
00
Event
Flag
-
Description
open-drain
Control
OUTPUT
Enable
DDRx
ORx
Bit
10
XX
= DDR, OR
from
Wait
Exit
Yes
OUTPUT
push-pull
11
from
Exit
Halt
Yes