33911 datasheet(26/45 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33911

FUNCTIONAL DEVICE OPERATIONS

OPERATIONAL MODES

RESET

To reset an MCU, the 33911 drives the RST pin low for the

time the reset condition lasts.

After the reset source has been removed, the state

machine will drive the RST output low for at least 1ms (typical

value) before driving it high.

In the 33911 four main reset sources exist:

5V Regulator Low-voltage-Reset (VRSTTH)

The 5V regulator output VDD is continuously monitored

against brown outs. If the supply monitor detects that the

voltage at the VDD pin has dropped below the reset threshold

VRSTTH the 33911 will issue a reset. In case of an over-

temperature, the voltage regulator will be disabled and the

voltage monitoring will issue a VDDOT Flag independently of

the VDD voltage.

Window Watchdog Overflow

If the watchdog counter is not properly serviced while its

window is open, the 33911 will detect an MCU software run-

away and will reset the microcontroller.

Wake-Up From Sleep Mode

During Sleep Mode, the 5V regulator is not active. Hence,

all wake-up requests from Sleep Mode require a power-up/

reset sequence.

External Reset

The 33911 has a bidirectional reset pin which drives the

device to a safe state (same as Reset Mode) for as long as

this pin is held low. The RST pin must be held low long

enough to pass the internal glitch filter and get recognized by

the internal reset circuit. This functionality is also active in

Stop Mode.

After the RST pin is released, there is no extra t RST to be

considered.

WAKE-UP CAPABILITIES

Once entered into one of the low-power modes (Sleep or

Stop) only wake-up sources can bring the device into Normal

Mode operation.

In Stop Mode, a wake-up is signaled to the MCU as an

interrupt, while in Sleep Mode, the wake-up is performed by

activating the 5V regulator and resetting the MCU. In both

cases, the MCU can detect the wake-up source by accessing

the SPI registers. There is no specific SPI register bit to signal

a CS wake-up or external reset. If necessary, this condition is

detected by excluding all other possible wake-up sources.

Wake-up from Wake-up inputs (L1-L2) with cyclic sense

disabled

The wake-up lines are dedicated to sense state changes

of external switches, and wake-up the MCU (in Sleep or Stop

Mode).

In order to select and activate direct wake-up from Lx

inputs, the Wake-up Control Register (WUCR) must be

configured with appropriate LxWE inputs enabled or

disabled. The wake-up inputs state are read through the

Wake-up Status Register (WUSR).

Lx inputs are also used to perform cyclic sense wake-up.

Note: Selecting an Lx input in the analog multiplexer

before entering low-power mode will disable the wake-up

capability of the Lx input.

Wake-up from Wake-up inputs (L1-L2) with cyclic sense

timer enabled

The SBCLIN can wake-up at the end of a cyclic sense

period if on one of the two wake-up input lines (L1-L2), a state

change occurs. The HS1 switch is activated in Sleep or Stop

Modes from an internal timer. Cyclic sense and force wake-

up are exclusive. If cyclic sense is enabled, the force wake-

up can not be enabled.

In order to select and activate the cyclic sense wake-up

from Lx inputs, before entering in low-power modes (Stop or

Sleep Modes), the following SPI set-up has to be performed:

• In WUCR: select the Lx input to WU-enable.

• In HSCR: enable HS1.

• In TIMCR: select the CS/WD bit and determine the

cyclic sense period with CYSTx bits.

• Perform Goto Sleep/Stop command.

Forced Wake-up

The 33911 can wake-up automatically after a

predetermined time spent in Sleep or Stop Mode. Cyclic

sense and forced wake-up are exclusive. If forced wake-up is

enabled, the cyclic sense can not be enabled.

To determine the wake-up period, the following SPI set-up

has to be sent before entering in low-power modes:

• In TIMCR: select the CS/WD bit and determine the low-

power mode period with CYSTx bits.

• In HSCR: the HS1 bit must be disabled.

CS Wake-up

While in Stop Mode, a rising edge on the CS will cause a

wake-up. The CS wake-up does not generate an interrupt

and is not reported on the SPI.

LIN Wake-up

While in the low-power mode the 33911 monitors the

activity on the LIN bus. A dominant pulse larger than tPROPWL

followed by a dominant to recessive transition will cause a

LIN wake-up. This behavior protects the system from a short-

to ground bus condition.

33911 Datasheet(PDF) 26 Page - Freescale Semiconductor, Inc

33911 Datasheet(HTML) 26 Page - Freescale Semiconductor, Inc

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