GS2986 datasheet(25/41 Pages) SEMTECH

25 / 41 page

GS2986 Multi-Rate SDI Reclocker with Equalization &

De-emphasis

Data Sheet

52134 - 3

July 2012

25 of 41

reading hard-wired pin configuration, pin override settings and the values of all status

monitoring pins.

There is an optional 3-state feature available in the Control Status Registers (CSR) that

puts the SPI SDO to high-impedance when it’s not being used (Register: TOP_1, bit: 2).

The maximum operating speed of the SPI is 10MHz.

4.15.2 Legacy Mode & Start-up

In legacy mode, basic configuration of the device including a subset of equalizer settings

are available at the pin level. In this mode, register settings are automatically set to

default so that the IC is live at power-up.

4.15.3 Host Interface Mode & Start-up

In host interface mode, the user gains access to Control and Status Registers (CSRs) that

manage advanced features. In this mode, equalizer and de-emphasis settings are set

through the CSR.

The SPI control port is functional at start-up without the need for a separate, external

reset signal. However, all internal registers must be set to their default state by issuing a

required Reset Command via the SPI.

This is done by setting the R bit (reset) LOW in the command word. This will guarantee

the CSR will not start up in a random state.

A simple way to issue the required reset of the CSR is to hold the slave device’s SDI input

LOW for an entire 64 cycle WRITE communication. Details of the WRITE operation are

found in section 4.15.6 below.

4.15.4 Clock & Data Timing

The SPI signals are Serial Data Input (SDI), Serial Data Output (SDO), active-low Chip

Select (CS), and Serial Clock Input (SCK). The host interface operates in SPI Mode 0, i.e.

the SDI input will latch data in on the rising edge of SCK. The SDO data output will

transition on falling edges of SCK. Data is transmitted or received on the SPI port MSB

first LSB last.

Figure 4-4: Data Clock Alignment

SCK

Cycle #

SDO

SDI

GS2986 Datasheet(PDF) 25 Page - Semtech Corporation