MMA81XXTKEG

Sensors

6

Freescale Semiconductor

1.3

PIN FUNCTIONS

The following paragraphs provide descriptions of the general function of each pin.

1.3.1

Power is supplied to the ASIC through BUSIN or BUSOUT and BUSRTN. The supply voltage is rectified internally and applied

connected to the BUSRTN node on the PWB. To ensure stability of the internal voltage regulator and meet DFMEA requirements,

printed wiring assembly.

a short word Read Acceleration Data command, and report the undervoltage condition by setting the Undervoltage (U) flag.

Should the undervoltage condition persist for more than one millisecond, the internal Power-On Reset (POR) circuit is activated

initialization.

1.3.2

BUSIN

The BUSIN pin is normally connected to the DSI bus and supports bidirectional communication with the master.

MMA81XXEG supports reverse initialization for improved system fault tolerance. In the event that the DSI bus cannot support

communication between the master and BUSIN pin, communication with the master may be conducted via the BUSOUT pin and

the BUSIN pin can be used to access other DSI devices.

1.3.3

BUSOUT

The BUSOUT pin is normally connected to the DSI bus for daisy-chained bus configurations. In support of fault tolerance at the

system level, the BUSOUT pin can be used as an input for reverse initialization and data communication.

The internal bus switch is always open following reset. The bus switch is closed when data bit D6 is set when an Initialization or

Reverse Initialization command is received.

1.3.4

BUSRTN

This pin provides the common return for power and signalling.

1.3.5

without excessive internal resistance or inductance. An optional electrolytic capacitor may be required if a longer power down

delay is required.

reliability.

Figure 1-3. Voltage Regulator Capacitance and Series Resistance

1

μF100 μF

ESR

STABLE

STABLE, UNACCEPTABLE

0

700 m

Ω

NOISE PERFORMANCE