ST72321B datasheet(49/187 Pages) STMICROELECTRONICS

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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 32 on page 49. Other

transitions are potentially risky and should be

avoided, since they are likely to present unwanted

side-effects such as spurious interrupt generation.

Figure 32. 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).

Mode

Description

WAIT

No effect on I/O ports. External interrupts

cause the device to exit from WAIT mode.

HALT

No effect on I/O ports. External interrupts

cause the device to exit from HALT mode.

Interrupt Event

Event

Flag

Enable

Control

Bit

Exit

from

Wait

Exit

from

Halt

External interrupt on

selected external

event

DDRx

ORx

Yes

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

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