GS2965 datasheet(29/41 Pages) SEMTECH

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GS2965 Multi-Rate SDI Reclocker with Equalization &

De-emphasis

Data Sheet

52462 - 4

July 2012

29 of 41

Proprietary & Confidential

4.15.8 Daisy Chain Operation

For applications with multiple GS2965 devices, it is possible to daisy-chain up to 127

parts in serial. In this configuration, the first device SDI should be connected to the SPI

Master SDO. The serial data output of each device is then connected to the serial data

input of the following device, and so on. The last device's SDO connects to the Master's

SDI. Connecting devices in serial reduces the number of I/O ports required by the master

by removing the need for additional chip select lines.

Figure 4-10: Daisy Chained SPI Bus

The position of each GS2965 device in the serial chain is referred to as its Chain Position,

with 0 corresponding to the first device. The Chain Position in the SPI command word is

decoded by each slave to know which device the master is talking to.

Each GS2965 slave is designed to output a replica of what it receives at its input after a

delay of 32 cycles. The Chain Position part of the command is decremented by one in the

duplicated command word at the output. Each device in the chain will only execute the

issued command if it verifies that the current chain position is set to 0.

Figure 4-11: Chain Position Decoding

SPI

Master

SCK

SDO

SDI

SPI

Slave

SCK

SDI

SDO

SCK

SDI

SDO

SCK

SDI

SDO

SPI

Slave

SPI

Slave

Chain Position 0

Chain Position 1

Chain Position 2

GS2965

SDI

SDO

Chain Position

-1

A[4:0]

Chain Position

A[4:0]

C[6:0]=N

32 cycles

GS2965

SDI

SDO

Chain Position

-2

32 cycles

C[6:0]=N-1

C[6:0]=N-2

A[4:0]

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