GS2985 Datasheet, PDF (33/45 Pages) Gennum Corporation – Uses standard 27MHz crystal

4.15.9 Read & Write Operation - Daisy Chained Devices
In a serial daisy chain configuration, Read and/or Write operations can be performed to
multiple devices in the chain via consecutive operations. Figure 4-12 below shows a simple 3
device configuration.
MISO
MOSI
µC
SDI SDO
GS2985
SDI SDO
GS2985
SDI SDO
GS2985
Figure 4-12: Three Devices in Daisy Chain Configuration
4.15.10 Writing to all Devices
When writing to all devices in the chain, a Write Command and corresponding Data is required
for each device. When the devices are being configured in the same way, all of them will have
the same command and data with the exception of the Chain Position bits. This example
assumes a 3-device daisy chain. A command is issued to the last device in the chain first,
although it is possible to talk to the devices in any order.
CS
MOSI ^{Command2 [15:0]}
Chain Position = 2
Data [15:0]
Command1 [15:0]
Chain Position = 1
Data [15:0]
Command0 [15:0]
Chain Position = 0
Data [15:0]
Data High 32 cycles
MISO
Command0' [15:0]
Data [15:0]
Figure 4-13: Daisy Chain Write
1. The first command issued in time is the command for the last device in the chain (chain
position = 2). When the first device receives this command it will recognize that the Chain
Position is 2 and will not execute the command. It will duplicate the command and data
word at its output and decrement the Chain Position by one.
2. Consecutive commands are issued for each device in the chain as shown.
GS2985 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
36663 - 5
July 2012
33 of 45
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