ST72C254G2 datasheet(34/135 Pages) STMICROELECTRONICS

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ST72104G, ST72215G, ST72216G, ST72254G

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I/O PORTS (Cont’d)

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 I-bit in the CC reg-

ister is reset (RIM instruction).

9.6 REGISTER DESCRIPTION

DATA REGISTER (DR)

Port x Data Register

PxDR with x = A, B or C.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = D[7:0]

Data register 8 bits.

The DR register has a specific behaviour accord-

ing to the selected input/output configuration. Writ-

ing the DR register is always taken into account

even if the pin is configured as an input; this allows

always having the expected level on the pin when

toggling to output mode. Reading the DR register

returns either the DR register latch content (pin

configured as output) or the digital value applied to

the I/O pin (pin configured as input).

DATA DIRECTION REGISTER (DDR)

Port x Data Direction Register

PxDDR with x = A, B or C.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = DD[7:0]

Data direction register 8 bits.

The DDR register gives the input/output direction

configuration of the pins. Each bit is set and

cleared by software.

0: Input mode

1: Output mode

OPTION REGISTER (OR)

Port x Option Register

PxOR with x = A, B or C.

Read/Write

Reset Value: 0000 0000 (00h)

Bit 7:0 = O[7:0]

Option register 8 bits.

For specific I/O pins, this register is not implement-

ed. In this case the DDR register is enough to se-

lect the I/O pin configuration.

The OR register allows to distinguish: in input

mode if the pull-up with interrupt capability or the

basic pull-up configuration is selected, in output

mode if the push-pull or open drain configuration is

selected.

Each bit is set and cleared by software.

Input mode:

0: Floating input

1: Pull-up input with or without interrupt

Output mode:

0: Output open drain (with P-Buffer unactivated)

1: Output push-pull (when available)

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

DD7

DD6

DD5

DD4

DD3

DD2

DD1

DD0

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