Daisy chain

AN4290

12/16

DocID024501 Rev 2

2

Daisy chain

The device is compatible with the daisy chain architecture allowing the MCU to drive

multiple devices with a single SPI interface.

The daisy chain architecture is obtained as follows:

–

Master serial clock line is connected to the CK input of all the slaves.

–

Master slave select line is connected to the CS input of all the slaves.

–

Master serial data output (MOSI) is connected to the SDI input of the first slave of

the chain.

–

The SDO output of each slave is connected to the SDI input of the next slave, last

slave of the chain excluded.

–

Master serial data input (MISO) is connected to the SDO output of the last slave of

the chain.

The connection diagram of the configuration is shown in Figure 8.

Figure 8. Daisy chain connection diagram

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

a number of bytes. At each communication cycle, 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: 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.

See Figure 9 as example of a daisy chain configuration with 3 slaves.

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

AM16752v1