ST7LITEUS5 datasheet(64/136 Pages) STMICROELECTRONICS

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9.6

I/O port implementation

The hardware implementation on each I/O port depends on the settings in the DDR and OR

registers and specific feature of the I/O port such as ADC Input 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 illustrated in Figure 29.

Other transitions are potentially risky and should be avoided, since they are likely to present

unwanted side-effects such as spurious interrupt generation.

Figure 29.

Interrupt I/O port state transitions

The I/O port register configurations are summarized in Table 22.

After reset, to configure PA3 as a general purpose output, the application has to program

the MUXCR0 and MUXCR1 registers. See Section 6.5: Register description on page 37

Table 22.

Port configuration

Port

Pin name

Input (DDR=0)

Output (DDR=1)

OR = 0

OR = 1

OR = 0

OR = 1

Port A

PA0:2,

PA4:5

floating

pull-up interrupt

open drain

push-pull

PA3

open drain

push-pull

Table 23.

I/O port register map and reset values

Address

(Hex.)

label

76543

210

0000h

PADR

Reset

value

MSB

00000

LSB

0001h

PADDR

Reset

value

MSB

00001

LSB

0002h

PAOR

Reset

value

MSB

00000

LSB

floating/pull-up

interrupt

INPUT

floating

(reset state)

INPUT

open-drain

OUTPUT

push-pull

OUTPUT

= DDR, OR

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