L9950 datasheet(10/23 Pages) STMICROELECTRONICS

10 / 23 page

L9950

10/23

FUNCTIONAL DESCRIPTION OF THE SPI

4.1

Serial Peripheral Interface (SPI)

This device uses a standard SPI to communicate with a microcontroller. The SPI can be driven by a mi-

crocontroller with its SPI peripheral running in following mode: CPOL = 0 and CPHA = 0.

For this mode, input data is sampled by the low to high transition of the clock CLK, and output data is

changed from the high to low transition of CLK.

This device is not limited to microcontroller with a build-in SPI. Only three CMOS-compatible output pins

and one input pin will be needed to communicate with the device. A fault condition can be detected by

setting CSN to low. If CSN = 0, the DO-pin will reflect the status bit 0 (fault condition) of the device which

is a logical-or of all bits in the status registers 0 and 1. The microcontroller can poll the status of the device

without the need of a full SPI-communication cycle.

Note:

In contrast to the SPI-standard the least significant bit (LSB) will be transferred first (see FIGURE 6).

4.2

Chip Select Not (CSN)

The input pin is used to select the serial interface of this device. When CSN is high, the output pin (DO)

will be in high impedance state. A low signal will activate the output driver and a serial communication can

be started. The state when CSN is going low until the rising edge of CSN will be called a communication

frame. If the CSN-input pin is driven above 7.5V, the L9950 will go into a test mode. In the test mode the

DO will go from tri-state to active mode.

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