Datasheet

DS1878
SFP+ Controller with Digital LDD Interface
______________________________________________________________________________________ 27
CSEL_OUT
SCLOUT
SDAOUT
CSEL_OUT
NOTE: SEE THE 3-WIRE DIGITAL INTERFACE SPECIFICATION TABLE FOR DETAILS. CSEL_OUT IMPLIES CSEL1OUT OR CSEL2OUT.
SCLOUT
SDAOUT
12345678
A6
9 1011121314150
1234567891011121314150
A5 A4 A3 A2 A1 RWN D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0RWN
WRITE MODE
READ MODE
A0
A6 A5 A4 A3 A2 A1 A0
t
L
t
CH
t
CL
t
CH
t
CL
t
L
t
DS
t
DH
t
DS
t
RS
t
DH
t
T
t
T
Figure 18. 3-Wire Timing
3-Wire Interface Timing
Figure 18 shows the 3-wire interface timing. Figure 19
shows the 3-wire state machine. See the 3-Wire Digital
Interface Specification table for more information.
DS1878 Master Communication
Interface
Normal Operation
The majority of the communications consist of bias
adjustments for the APC loop. After each temperature
conversion, the laser modulation setting must be updat-
ed. All registers are rewritten after every temperature
conversion. Status registers TXSTAT1 and TXSTAT2 are
read between temperature updates at a regular inter-
val, t
RR
(see the Analog Voltage Monitoring
Characteristics table). The results are stored in 3W
TXSTAT1 and 3W TXSTAT2 (Table 02h, FCh–FDh). Two
chip selects are provided: CSEL1OUT and CSEL2OUT.
In the case where a separate limiting amplifier and
laser driver are used, CSEL2OUT should be connected
to the limiting amplifier. CSEL2OUT is only active when
receiver-related registers are accessed. This minimizes
noise caused by the digital interface.
Manual Operation
The master interface is controllable using four registers in
the device: 3WCTRL, ADDRESS, WRITE, and READ.
Commands can be manually issued while the device is
in normal operation mode. It is also possible to suspend
normal 3-wire commands so that only manual operation
commands are sent (3WCTRL, Table 02h, Register F8h).
Initialization
During initialization, the device transfers all its 3-wire
EEPROM control registers to a Maxim laser driver and
limiting amplifier. The 3-wire control registers include
the following:
• RXCTRL1
• RXCTRL2
• SETCML
• SETLOS
• TXCTRL
• IMODMAX
• IBIASMAX
• SETPWCTL
• SETTXDE
• SETTXEQ
• SETLOSTIMER
• RXCTRL3
• TXCTRL2
• TXCTRL3