Rainbow Electronics MAX6641 - Manual (Page 8)

MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
8 _______________________________________________________________________________________
Write Byte Format
Read Byte Format
Send Byte Format Receive Byte Format
Slave address: equiva-
lent to chip-select line of
a 3-wire interface Command byte: selects which
register you are writing to Data byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave address: equivalent
to chip-select line Command byte: selects
which register you are
reading from Slave address: repeated
due to change in data-
flow direction Data byte: reads from
the register set by the
command byte
Command byte: sends com-
mand with no data, usually
used for one-shot command
Data byte: reads data from
the register commanded
by the last read byte or
write byte transmission;
also used for SMBus alert
response return address
S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged
Figure 1. SMBus Protocols
S ADDRESS RD ACK DATA /// P
7 bits 8 bits
WR S ACK COMMAND ACK P
8 bits
ADDRESS
7 bits
P
1
ACK DATA
8 bits
ACK COMMAND
8 bits
ACK WR ADDRESS
7 bits
S
S ADDRESS WR ACK COMMAND ACK S ADDRESS
7 bits 8 bits 7 bits
RD ACK DATA
8 bits
/// P
SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
A B C D E F G H I J
SMBDATA
t SU:STA t HD:STA
t LOW t HIGH
t SU:DAT
t SU:STO t BUF
L M K
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram