The L6480 and L6482 communication interface

AN4355

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The connection diagram of the configuration is shown in Figure 1.

Figure 1.

Daisy chain connection diagram

In this configuration, the chain of slaves acts as a single slave with an SPI device of N byte.

Each communication cycle, for example when the master needs to transmit/receive a byte

from/to a slave, the master must fill all the shift registers of the slaves before raising the CS

line.

The devices are addressed according to the position of the byte in the communication cycle:

the first byte transmitted by the master is received by the last device of the chain; the

second one is received by the last-but-one slave and so on down to the last transmitted byte

which is received by the first slave of the chain. The response bytes from the device chain

are addressed to the same way: the first byte received by the master has been transmitted

by the last device of the chain; the second one has been transmitted by the last-but-one

slave and so on down to the last received byte which has been transmitted by the first slave

of the chain.

In theory, the number of slaves that an MCU can drive using the daisy chain configuration is

unlimited; in practice the maximum number of devices connected to the same SPI depends

on the clock skew.

The number of slaves limits the communication speed also because every time a byte has

to be transmitted to a device, the whole N slave chain has to be filled transmitting N - 1 extra

bytes.

MCU

Serial clock

Slave select

Serial data out

Serial data in

Device 1 (1st of the chain)

to SDI of

device 2

to SDI of

device X+2

from SDO of

device X -1

from SDO of

device N -1

Device X

Device X+1

Device N (last of the chain)

CS

CK

SDI

SDO

CS

CK

SDI

SDO

CS

CK

SDI

SDO

CS

CK

SDI

SDO

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