DS1874 datasheet(22/88 Pages) MAXIM

22 / 88 page

same signals and faults can also be used to generate

the internal signal FETG (Table 01h/05h, Registers FAh

and FBh). FETG is used to send a fast “turn-off” com-

mand to the laser driver. The intended use is a direct

connection to the MAX3798/MAX3799’s TXD input if

this is desired. When VCC < POA, TXDOUT is high

impedance.

Transmit Fault (TXF) Output

TXF can be triggered by all alarms, warnings, and

quick trips (Figure 12). The six ADC alarms, warnings,

and the LOS quick trips require enabling (Table

01h/05h, Registers F8h and FDh). See Figures 14a and

14b for nonlatched and latched operation. Latching of

the alarms is controlled by the CNFGB and CNFGC

registers (Table 02h, Registers 8Ah–8Bh).

Die Identification

The DS1874 has an ID hardcoded in its die. Two regis-

ters (Table 02h, Registers CEh–CFh) are assigned for

this feature. The CEh register reads 74h to identify the

part as the DS1874, while the CFh register reads the

current device version.

3-Wire Master for Controlling

the MAX3798/MAX3799

The DS1874 controls the MAX3798/MAX3799 over a

proprietary 3-wire interface. The DS1874 acts as the

master, initiating communication with and generating

the clock for the MAX3798/MAX3799. It is a 3-pin inter-

face consisting of SDAOUT (a bidirectional data line),

an SCLOUT clock signal, and a CSELOUT chip-select

output (active high).

Protocol

The DS1874 initiates a data transfer by asserting the

CSELOUT pin. It then starts to generate a clock signal

______________________________________________________________________________________

DETECTION OF TXF FAULT

TXD

TXF

Figure 14b. TXF Latched Operation

INVOUT1

IN1C

IN1

IN1S

OUT1

INV LOS

LOSC

MUX

LOSOUT

RSELOUT

RSELC

RSEL

LOS

LOS LO

RSELS

RXL

SFP+ Controller with Digital LDD Interface

DETECTION OF TXF FAULT

TXF

Figure 14a. TXF Nonlatched Operation

Figure 13. Logic Diagram 2

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