L6474 datasheet(30/51 Pages) STMICROELECTRONICS

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Serial interface

L6474

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Doc ID 022529 Rev 2

Serial interface

The integrated 8-bit serial peripheral interface (SPI) is used for a synchronous serial

communication between the host microprocessor (always master) and the L6474 (always

slave).

The SPI uses chip select (CS), serial clock (CK), serial data input (SDI) and serial data

output (SDO) pins. When CS is high, the device is unselected and the SDO line is inactive

(high-impedance).

The communication starts when CS is forced low. The CK line is used for synchronization of

data communication.

All commands and data bytes are shifted into the device through the SDI input, most

significant bit first. The SDI is sampled on the rising edges of the CK.

All output data bytes are shifted out of the device through the SDO output, most significant

bit first. The SDO is latched on the falling edges of the CK. When a return value from the

device is not available, an all zero byte is sent.

After each byte transmission, the CS input must be raised and be kept high for at least

tdisCS in order to allow the device to decode the received command and put the return

value into the shift register.

All timing requirements are shown in Figure 13 (see respective Section 3: Electrical

characteristics for values).

Multiple devices can be connected in a daisy-chain configuration, as shown in Figure 14.

Figure 13.

SPI timings diagram

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