Owner's manual

after the CSELOUT has been set to 1. Each operation
consists of 16-bit transfers (15-bit address/data, 1-bit
RWN). All data transfers are MSB first.
Write Mode (RWN = 0): The master generates 16 clock
cycles at SCLOUT in total. It outputs 16 bits (MSB first)
to the SDAOUT line at the falling edge of the clock. The
master closes the transmission by setting the
CSELOUT to 0.
Read Mode (RWN = 1): The master generates 16 clock
cycles at SCLOUT in total. It outputs 8 bits (MSB first)
to the SDAOUT line at the falling edge of the clock. The
SDAOUT line is released after the RWN bit has been
transmitted. The slave outputs 8 bits of data (MSB first)
at the rising edge of the clock. The master samples
SDAOUT at the falling edge of SCLOUT. The master
closes the transmission by setting the CSELOUT to 0.
3-Wire Interface Timing
Figure 15 shows the 3-wire interface timing. Figure 16
shows the 3-wire state machine. See the 3-Wire Digital
Interface Specification
table for more information.
DS1874 and MAX3798/MAX3799
Communication
Normal Operation
The majority of the communication between the two
devices consists of bias adjustments for the APC loop.
After each temperature conversion, the laser modula-
tion setting must be updated. Status registers TXSTAT1
and TXSTAT2 are read between temperature updates
at a regular interval: t
RR
(see the Electrical Characteristics
table). The results are stored in TXSTAT1 and TXSTAT2
(Table 02h, F4h–F5h).
Manual Operation
The MAX3798/MAX3799 are manually controllable
using four registers in the DS1874: 3WCTRL,
ADDRESS, WRITE, and READ. Commands can be
manually issued while the DS1874 is in normal opera-
tion mode. It is also possible to suspend normal 3-wire
commands so that only manual operation commands
are sent (3WCTRL, Table 02h, Register F8h).
DS1874
SFP+ Controller with Digital LDD Interface
______________________________________________________________________________________ 23
BIT NAME DESCRIPTION
15:9 Address 7-bit internal register address
8 RWN 0: write; 1: read
7:0 Data 8-bit read or write data
CSELOUT
SCLOUT
SDAOUT
CSELOUT
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
L
t
DS
t
DH
t
DS
t
DH
t
T
t
T
Figure 15. 3-Wire Timing