GS2965 Datasheet, PDF (29/41 Pages) Gennum Corporation – Uses standard 27MHz crystal

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.
SPI
Master
SCK
SDO
SDI
CS
SCK
SDI
SDO
SPI
Slave
Chain Position 0
CS
SCK
SDI
SDO
SPI
Slave ^{Chain Position 1}
CS
SCK
SDI
SDO
CS
Figure 4-10: Daisy Chained SPI Bus
SPI
Slave
Chain Position 2
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.
A[4:0]
C[6:0]=N
Chain Position
32 cycles
SDI SDO
GS2965
A[4:0] C[6:0]=N-1
Chain Position
-1
32 cycles
SDI SDO
GS2965
A[4:0] C[6:0]=N-2
Chain Position
-2
Figure 4-11: Chain Position Decoding
GS2965 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
52462 - 4
July 2012
29 of 41
Proprietary & Confidential