Analog Devices ADT7460 Manual page 14

ADT7460
For the ADT 7460, the send byte protocol is used to write to the
address pointer register for a subsequent single-byte read from
the same address. This is illustrated in Figure 21.
1 2
SLAVE
S W A
ADDRESS
Figure 21. Settin g a Register Address for Subsequent Read
If it is required to read data from the register immediat
set tin g up the address, the master can assert a repeat st
con ition immediately after the final ACK a d
single-byte read without asserting an intermediate stop
con ition. d
Wr te Byte i
In t is operation, the master device s h
one data byte to the slave device as follows:
1. The master d evice asserts a start condition on SDA.
2. The master sends the 7-bit
write bit (low).
3. The addressed slave device asserts ACK on SDA.
4. The maste r sends the register address.
5. The slave assert s ACK on SDA.
6. The master sends a data byte.
7. The slave asserts ACK on SDA.
8. The master asserts a stop condition on SDA to end the
transaction.
This is illustrated i n Figure 22.
1 2 3
SLAVE REGISTER
S W A
ADDRESS
Figure 22. Single-Byte Write to a Register
Read Operations
The ADT7460 uses the following SMB
Rec ive Byte e
This is useful when repeatedly reading a single register. Th
regis ter address needs to have been set up previously. In this
operation, the master device receives a single byte from a slave
device as follows:
1. The master device asserts a start condition on SD
2. The master sends the 7-bit ave address followed by the
read bit ( high).
3 4 5 6
REGISTER
A P
ADDRESS
ely after
art
nd carry out a
ends a command byte and
slave address followed by the
4 5 6 7 8
A DATA A P
ADDRESS
us read protocols.
A.
sl
3. The addressed slave de
4. The master receives a data byte.
5. The master asserts NO ACK on SD
6. The master asserts a stop condition on SDA and the
transaction ends.
In the ADT7460, the receive byte protocol is used to read a
single byte of data from a register whose address has previously
been set by a send byte or by write byte operation.
Alert Response Address
Ale t response address (ARA) is a feature of SMBus devices tha r
allow s an interrupting device to identify itself to the host when
mul tiple devices exist on the same bus.
The SMBALERT output can be used as an interrupt output or
can be used as an SMBALERT . One or more outputs can be
conn ected to a common
mas ter. If a device's
occurs:
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the alert
response address (ARA = 0001 100). This is a general call
address, which must not be used as a specific device
address.
3. The device whose SMBALERT output is low responds to
the alert response address, and the master reads its device
address. The address of the device is now known, and it
can be interrogated in the usual way.
4. If more than one device's SMBALERT output is low, the
one with the lowest device address has priority in
accordance with normal SMBus arbitration.
5. Once the ADT7460 has responded to the alert response
address, the master must read the status registers and the
SMBALERT is cleared only if the error condition has gone
e
away.
Rev. C | Page 14 of 52
vice asserts ACK on SDA.
A.
1 2 3 4 5
SLAVE REGISTER
S W A A P
ADDRESS ADDRESS
Figure 23. Single-Byte Read from a Register
SMBALERT line connected to
SMBALERT line goes low, the following
6
t
the