MM908E624ACEWSLASHR2 datasheet(27/40 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

908E624

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

WINDOW WATCHDOG

The window watchdog is configurable using an external

resistor at the WDCONF terminal. The watchdog is cleared

through by the MODE1:2 bits in the SPI Control register (refer

to Table 8, page 29).

A watchdog clear is only allowed in the open window. If the

watchdog is cleared in the closed window or has not been

cleared at the end of the open window, the watchdog will

generate a reset on the RST_A terminal and reset the whole

device.

Note

The watchdog clear in Normal request mode

(150 ms) (first watchdog clear) has no window.

Figure 16. Window Watchdog Operation

Watchdog Configuration

If the WDCONF terminal is left open, the default watchdog

period is selected (typ. 150 ms). If no watchdog function is

required, the WDCONF terminal must be connected to GND.

The watchdog period is calculated using the following

formula:

tPWD [ms] = 0.991 * REXT [kΩ] + 0.648

VOLTAGE REGULATOR

The 908E624 chip contains a low-power, low dropout

voltage regulator to provide internal power and external

power for the MCU. The on-chip regulator consist of two

elements, the main voltage regulator and the low-voltage

reset circuit.

The VDD regulator accepts an unregulated input supply

and provides a regulated VDD supply to all digital sections of

the device. The output of the regulator is also connected to

the VDD terminal to provide the 5.0 V to the microcontroller.

Current Limit (Over-current) Protection

The voltage regulator has current limit to protect the device

against over-current and short circuit conditions.

Over-temperature Protection

The voltage regulator also features an over-temperature

protection having an over-temperature warning (Interrupt -

VDDT) and an over-temperature shutdown.

Stop Mode

During Stop mode, the Stop mode regulator supplies a

regulated output voltage. The Stop mode regulator has a

limited output current capability.

Sleep Mode

In Sleep mode the voltage regulator external VDD is turned

off.

FACTORY TRIMMING AND CALIBRATION

To enhance the ease-of-use of the 908E624, various

parameters (e.g., ICG trim value) are stored in the flash

memory of the device. The following flash memory locations

are reserved for this purpose and might have a value different

from the “empty” (0xFF) state:

• 0xFD80:0xFDDF Trim and Calibration Values

• 0xFFFE:0xFFFF Reset Vector

In the event the application uses these parameters, one

has to take care not to erase or override these values. If these

parameters are not used, these flash locations can be erased

and otherwise used.

Trim Values

The usage of the trim values, located in the flash memory,

is explained in the following.

Internal Clock Generator (ICG) Trim Value

The internal clock generator (ICG) module is used to

create a stable clock source for the microcontroller without

using any external components. The untrimmed frequency of

the low-frequency base clock (IBASE), will vary as much as

±25 percent due to process, temperature, and voltage

dependencies. To compensate for these dependencies, an

ICG trim value is located at address $FDC2. After trimming

the ICG, a range of typ. ±2% (±3% max.) at nominal

conditions (filtered (100nF) and stabilized (4,7uF) VDD = 5V,

TAmbient~23°C) and will vary over-temperature and voltage

(VDD) as indicated in the 68HC908EY16 data sheet.

To trim the ICG, these values have to be copied to the ICG

Trim Register ICGTR at address $38 of the MCU.

Important

The value has to be copied after every reset.

OPERATING MODES OF THE MCU

For a detailed description of the operating modes of

the MCU, refer to the MC68HC908EY16 data sheet.

Window closed

no watchdog clear allowed

Window open

for watchdog clear

WD timing x 50%

WD period (PWD)

WD timing selected by resistor on WDCONF terminal.

(tPWD)

MM908E624ACEW/R2 Datasheet(PDF) 27 Page - Freescale Semiconductor, Inc

MM908E624ACEW/R2 Datasheet(HTML) 27 Page - Freescale Semiconductor, Inc

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