ST7L09 datasheet(40/104 Pages) STMICROELECTRONICS

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ST7L05, ST7L09

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I/O PORTS (Cont’d)

Caution: The alternate function must not be acti-

vated as long as the pin is configured as input with

interrupt, in order to avoid generating spurious in-

terrupts.

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.

10.3 UNUSED I/O PINS

Unused I/O pins must be connected to fixed volt-

age levels. Refer to Section 13.8.

10.4 LOW POWER MODES

10.5 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).

10.6 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.

Switching these I/O ports from one state to anoth-

er must be done in a sequence that prevents un-

wanted side effects. Recommended safe transi-

tions are illustrated in Figure 24 Other transitions

are potentially risky and should be avoided, since

they are likely to present unwanted side-effects

such as spurious interrupt generation.

Figure 24. Interrupt I/O Port State Transitions

The I/O port register configurations are summa-

rized as follows:

Table 11. Port Configuration

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

XX = DDR, OR

Port

Pin name

Input (DDR = 0)

Output (DDR = 1)

OR = 0

OR = 1

OR = 0

OR = 1

Port A

PA7

floating

pull-up interrupt

open drain

push-pull

PA6:1

pull-up

PA0

pull-up interrupt

Port B

PB4

pull-up

PB3

pull-up interrupt

PB2:1

pull-up

PB0

pull-up interrupt

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