ST7FL15F1MCE datasheet(44/138 Pages) STMICROELECTRONICS

44 / 138 page

ST7L15, ST7L19

44/138

I/O PORTS (cont’d)

– Set the interrupt mask with the SIM instruction

SIM (in cases where a pin level change could

occur)

– Select falling edge

– Disable the external interrupt through the OR

– Select rising edge

– Reset the interrupt mask with the RIM instruc-

tion (in cases where a pin level change could

occur)

10.2.2 Output Modes

Setting the DDRx bit selects output mode. Writing

to the DR bits applies a digital value to the I/O

through the latch. Reading the DR bits returns the

previously stored value.

If an OR bit is available, different output modes

can be selected by software: Push-pull or open-

drain. Refer to “I/O PORT IMPLEMENTATION” on

page 47 for configuration.

DR Value and Output Pin Status

10.2.3 Alternate Functions

Many ST7 I/Os have one or more alternate func-

tions. These may include output signals from, or

input signals to, on-chip peripherals. The Device

Pin Description table describes which peripheral

signals can be input/output to which ports.

A signal coming from an on-chip peripheral can be

output on an I/O. To do this, enable the on-chip

peripheral as an output (enable bit in the peripher-

al’s control register). The peripheral configures the

I/O as an output and takes priority over standard I/

O programming. The I/O’s state is readable by ad-

dressing the corresponding I/O data register.

Configuring an I/O as floating enables alternate

function input. It is not recommended to configure

an I/O as pull-up as this increases current con-

sumption. Before using an I/O as an alternate in-

put, configure it without interrupt. Otherwise spuri-

ous interrupts can occur.

Configure an I/O as input floating for an on-chip

peripheral signal which can be input and output.

Caution: I/Os which can be configured as both an

analog and digital alternate function need special

attention. The user must control the peripherals so

that the signals do not arrive at the same time on

the same pin. If an external clock is used, only the

clock alternate function should be employed on

that I/O pin and not the other alternate function.

Push-Pull

Open-Drain

0VOL

VOL

1VOH

Floating

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