Rainbow Electronics MAX5970 - Manual (Page 38)

0V to 16V, Dual Hot-Swap Controller with 10-Bit
Current and Voltage Monitor and 4 LED Drivers
MAX5970
38 _____________________________________________________________________________________
Figure 7. SMBUS/I 2 C Protocols
START and STOP Conditions
Both SCL and SDA idle high when the bus is not busy.
A master device signals the beginning of a transmission
with a START condition (see Figure 3) by transitioning
SDA from high to low while SCL is high. The master
device issues a STOP condition (see Figure 6) by transi-
tioning SDA from low to high while SCL is high. A STOP
condition frees the bus for another transmission. The bus
remains active if a REPEATED START condition is gener-
ated, such as in the block read protocol (see Figure 7).
WRITE BYTE FORMAT
S
S
ADDRESS
ADDRESS
7 BITS
7 BITS
SEND BYTE FORMAT
RECEIVE BYTE FORMAT
WR
WR
ACK
ACK
DATA
DATA
8 BITS
8 BITS
ACK P
ACK P
DATA BYTE–PRESETS THE
INTERNAL ADDRESS POINTER.
DATA BYTE–READS DATA FROM
THE REGISTER COMMANDED BY
THE LAST READ BYTE OR WRITE
BYTE TRANSMISSION. ALSO
DEPENDENT ON A SEND BYTE.
WRITE WORD FORMAT
S ADDRESS WR ACK ACK ACK ACK COMMAND DATA DATA P
7 BITS 8 BITS 8 BITS 8 BITS
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
COMMAND BYTE–
MSB OF THE
EEPROM
REGISTER BEING
WRITTEN.
DATA BYTE–FIRST BYTE IS THE LSB OF
THE EEPROM ADDRESS. SECOND
BYTE IS THE ACTUAL DATA.
BLOCK WRITE FORMAT
S ADDRESS WR ACK COMMAND ACK
BYTE
COUNT= N
ACK
DATA BYTE
1
ACK
DATA BYTE
...
ACK
DATA BYTE
N
ACK P
7 BITS 8 BITS 8 BITS 8 BITS 8 BITS
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
COMMAND BYTE–
PREPARES DEVICE
FOR BLOCK
OPERATION.
DATA BYTE–DATA GOES INTO THE REGISTER SET BY THE
COMMAND BYTE.
BLOCK READ FORMAT
S ADDRESS WR ACK COMMAND ACK SR ADDRESS WR ACK
8 BITS
BYTE
COUNT= 16
ACK
DATA BYTE
1
ACK
DATA BYTE
...
ACK
DATA BYTE
N
ACK P
7 BITS 8 BITS 7 BITS 10h 8 BITS 8 BITS 8 BITS
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
COMMAND BYTE–
PREPARES DEVICE
FOR BLOCK
OPERATION.
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
DATA BYTE–DATA GOES INTO THE REGISTER SET BY THE
COMMAND BYTE.
S = START CONDITION
P = STOP CONDITION SHADED = SLAVE TRANSMISSION
Sr = REPEATED START CONDITION
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
S ADDRESS WR ACK COMMAND ACK DATA ACK P
7 BITS 8 BITS 8 BITS
SLAVE ADDRESS–
EQUIVALENT TO CHIP-
SELECT LINE OF A
3-WIRE INTERFACE.
COMMAND BYTE–
SELECTS REGISTER
BEING WRITTEN. DATA BYTE–DATA GOES INTO THE
REGISTER SET BY THE COMMAND
BYTE IF THE COMMAND IS BELOW
50h. IF THE COMMAND IS 80h,
81h, or 82h, THE DATA BYTE
PRESETS THE LSB OF AN EEPROM
ADDRESS.
1 0
0
0 0
1 0