Rainbow Electronics DS1874 - Manual (Page 28)

DS1874
SFP+ Controller with Digital LDD Interface
28 ______________________________________________________________________________________
START
START STOP
SLAVE
ACK
SLAVE
ACK
STOP
SINGLE-BYTE WRITE
-WRITE 00h TO REGISTER BAh
TWO-BYTE WRITE
-WRITE C8h AND C9h
TO 01h AND 75h
SINGLE-BYTE READ
-READ REGISTER BAh
TWO-BYTE READ
-READ C8h AND C9h
REPEATED
START
MASTER
NACK
1 0 1 0 0 0 1 0
A2h
1 0 1 1 1 0 1 0
BAh
SLAVE
ACK
START
SLAVE
ACK
1 0 1 0 0 0 1 0
A2h
1 0 1 0 0 0 1 1
A3h
1 0 1 1 1 0 1 0
BAh
SLAVE
ACK
SLAVE
ACK
STOP
0 0 0 0 0 0 0 0
00h
STOP
SLAVE
ACK
STOP
0 1 1 1 0 1 0 1
75h
START
SLAVE
ACK
1 0 1 0 0 0 1 0
A2h
1 1 0 0 1 0 0 0
C8h
SLAVE
ACK
SLAVE
ACK
0 0 0 0 0 0 0 1
01h
SLAVE
ACK
DATA IN BAh
DATA
REPEATED
START
MASTER
NACK
START
SLAVE
ACK
1 0 1 0 0 0 1 0
A2h
1 0 1 0 0 0 1 1
A3h
1 1 0 0 1 0 0 0
C8h
SLAVE
ACK
SLAVE
ACK
DATA IN C8h
DATA
MASTER
NACK
DATA IN C9h
DATA
EXAMPLE I 2 C TRANSACTIONS WITH A2h AS THE MAIN MEMORY DEVICE ADDRESS
*IF ASEL IS 0, THE SLAVE ADDRESS IS A0h FOR THE AUXILIARY MEMORY AND A2h FOR THE MAIN MEMORY.
IF ASEL = 1, THE SLAVE ADDRESS IS DETERMINED BY TABLE 02h, REGISTER 8Ch FOR THE MAIN MEMORY. THE AUXILIARY MEMORY CONTINUES TO BE ADDRESSED AT A0h, EXCEPT WHEN THE PROGRAMMED
ADDRESS FOR THE MAIN MEMORY IS A0h.
TYPICAL I 2 C WRITE TRANSACTION
A)
C)
B)
D)
MSB LSB
b7 b6 b5 b4 b3 b2 b1 b0
REGISTER ADDRESS
MSB LSB
b7 b6 b5 b4 b3 b2 b1 b0
DATA
SLAVE
ACK
SLAVE
ACK
SLAVE
ADDRESS*
1 0 1 0 0 0 1 R/W
MSB LSB
READ/
WRITE
Figure 18. Example I 2 C Timing
cycle. This can result in a whole page being worn out
over time by writing a single byte repeatedly. Writing
a page one byte at a time wears the EEPROM out
eight times faster than writing the entire page at
once. The DS1874’s EEPROM write cycles are speci-
fied in the
Nonvolatile Memory Characteristics table.
The specification shown is at the worst-case temper-
ature. It can handle approximately ten times that
many writes at room temperature. Writing to SRAM-
shadowed EEPROM memory with SEEB = 1 does not
count as an EEPROM write cycle when evaluating
the EEPROM’s estimated lifetime.
Reading a single byte from a slave: Unlike the
write operation that uses the memory address byte
to define where the data is to be written, the read
operation occurs at the present value of the memory
address counter. To read a single byte from the
slave, the master generates a START condition,
writes the slave address byte with R/W = 1, reads
the data byte with a NACK to indicate the end of the
transfer, and generates a STOP condition.
Manipulating the address counter for reads: A
dummy write cycle can be used to force the address
pointer to a particular value. To do this, the master
generates a START condition, writes the slave
address byte (R/W = 0), writes the memory address
where it desires to read, generates a repeated
START condition, writes the slave address byte (R/W
= 1), reads data with ACK or NACK as applicable,
and generates a STOP condition.
Memory Organization
The DS1874 features nine separate memory tables that
are internally organized into 8-byte rows.
The Lower Memory is addressed from 00h to 7Fh and
contains alarm and warning thresholds, flags, masks,
several control registers, password entry area (PWE),
and the table-select byte.
Table 01h primarily contains user EEPROM (with PW1
level access) as well as alarm and warning-enable
bytes.
Table 02h is a multifunction space that contains config-
uration registers, scaling and offset values, passwords,
interrupt registers as well as other miscellaneous con-
trol bytes.
Table 04h contains a temperature-indexed LUT for
control of the modulation voltage. The modulation LUT
can be programmed in 2°C increments over the -40°C
to +102°C range.