Functional description of the SPI

L9954 / L9954XP

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Doc ID 14279 Rev 4

content of the selected status register into the data out shift register. Each subsequent

falling edge of the CLK will shift the next bit out.

4.5

Serial clock (CLK)

The CLK input is used to synchronize the input and output serial bit streams. The data input

(DI) is sampled at the rising edge of the CLK and the data output (DO) will change with the

falling edge of the CLK signal.

4.6

Input data register

The device has two input registers. The first bit (bit 0) at the DI-input is used to select one of

the two Input Registers. All bits are first shifted into an input shift register. After the rising

edge of CSN the contents of the input shift register will be written to the selected Input Data

Register only if a frame of exact 24 data bits are detected. Depending on bit 0 the contents

of the selected status register will be transferred to DO during the current communication

frame. Bit 1-17 controls the behavior of the corresponding driver.

If bit 23 is zero, the device will go into the standby-mode. The bits 18 and 19 are used to

control the current monitor multiplexer. Bit 22 is used to reset all status bits in both status

registers. The bits in the status registers will be cleared after the current communication

frame (rising edge of CSN).

4.7

Status register

This devices uses two status registers to store and to monitor the state of the device. No

error bit (bit 0) is used as a fault bit and is a logical-NOR combination of bits 1-22 in both

status registers. The state of this bit can be polled by the microcontroller without the need of

a full SPI-communication cycle. If one of the over-current bits is set, the corresponding

driver will be disabled. If the over-current recovery bit of the output is not set the

microcontroller has to clear the over-current bit to enable the driver. If the thermal shutdown

bit is set, all drivers will go into a high impedance state. Again the microcontroller has to

clear the bit to enable the drivers.