Datasheet

ADM1066
Rev. E | Page 28 of 32
9
04609-037
19 91
191
START BY
MASTER
ACK. BY
SLAVE
ACK. BY
MASTER
ACK. BY
MASTER
NO ACK.
FRAME 2
DATA BYTE
FRAME 1
SLAVE ADDRESS
FRAME N
DATA BYTE
FRAME 3
DATA BYTE
SCL
SDA
R/W
STOP
BY
MASTER
SCL
(CONTINUED)
SDA
(CONTINUED)
D7A0A11110 0 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1
D0
D7 D6 D5 D4 D3 D2 D1 D0
Figure 37. General SMBus Read Timing Diagram
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SCL
SDA
PS S P
t
SU;STO
t
HD;STA
t
SU;STA
t
SU;DAT
t
HD;DAT
t
HD;STA
t
HIGH
t
BUF
t
LOW
t
R
t
F
Figure 38. Serial Bus Timing Diagram
SMBus PROTOCOLS FOR RAM AND EEPROM
The ADM1066 contains volatile registers (RAM) and nonvolatile
registers (EEPROM). User RAM occupies Address 0x00 to
Address 0xDF; the EEPROM occupies Address 0xF800 to
Address 0xFBFF.
Data can be written to and read from both the RAM and the
EEPROM as single data bytes. Data can be written only to
unprogrammed EEPROM locations. To write new data to a
programmed location, the location contents must first be erased.
EEPROM erasure cannot be done at the byte level. The EEPROM
is arranged as 32 pages of 32 bytes each, and an entire page
must be erased.
Page erasure is enabled by setting Bit 2 in the UPDCFG register
(Address 0x90) to 1. If this bit is not set, page erasure cannot
occur, even if the command byte (0xFE) is programmed across
the SMBus.
WRITE OPERATIONS
The SMBus specification defines several protocols for different
types of read and write operations. The following abbreviations
are used in Figure 39 to Figure 47:
• S = Start
• P = Stop
• R = Read
• W = Write
• A = Acknowledge
•
A
= No acknowledge
The ADM1066 uses the following SMBus write protocols.
Send Byte
In a send byte operation, the master device sends a single
command byte to a slave device, as follows:
1.
The master device asserts a start condition on SDA.
2.
The master sends the 7-bit slave address followed by the
write bit (low).
3.
The addressed slave device asserts an acknowledge (ACK)
on SDA.
4.
The master sends a command code.
5.
The slave asserts an ACK on SDA.
6.
The master asserts a stop condition on SDA, and the
transaction ends.
In the ADM1066, the send byte protocol is used for two
purposes:
• To write a register address to the RAM for a subsequent
single byte read from the same address, or for a block read
or block write starting at that address, as shown in Figure 39.
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2413 5
SLAVE
ADDRESS
RAM
ADDRESS
(0x00 TO 0xDF)
SWA A
6
P
Figure 39. Setting a RAM Address for Subsequent Read
• To erase a page of EEPROM memory. EEPROM memory
can be written to only if it is unprogrammed. Before writing
to one or more EEPROM memory locations that are already
programmed, the page(s) containing those locations must
first be erased. EEPROM memory is erased by writing a
command byte.