EVAL-ADT7490EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-ADT7490EBZ' PDF : 76 Pages View PDF
Send Byte
In this 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 ACK on SDA.
4. The master sends a command code.
5. The slave asserts ACK on SDA.
6. The master asserts a stop condition on SDA and the
transaction ends.
For the ADT7490, the send byte protocol is used to write a
register address to RAM for a subsequent single-byte read from
the same address. This operation is illustrated in Figure 22.
1
2
3
4
56
S
SLAVE
ADDRESS
W
A
REGISTER
ADDRESS
AP
Figure 22. Setting a Register Address for Subsequent Read
If the master is required to read data from the register immedi-
ately after setting up the address, it can assert a repeat start
condition immediately after the final ACK and carry out a
single-byte read without asserting an intermediate stop
condition.
Write Byte
In this operation, the master device sends a command byte and
one data byte to the 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 ACK on SDA.
4. The master sends a command code.
5. The slave asserts 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, and the
transaction ends.
The byte write operation is illustrated in Figure 23.
1
2
3
4
5 6 78
S
SLAVE
ADDRESS
W
A
REGISTER
ADDRESS
A
DATA
AP
Figure 23. Single Byte Write to a Register
ADT7490
READ OPERATIONS
The ADT7490 uses the following SMBus read protocols.
Receive Byte
This operation is useful when repeatedly reading a single
register. The register address must be previously set up. 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 SDA.
2. The master sends the 7-bit slave address followed by the
read bit (high).
3. The addressed slave device asserts ACK on SDA.
4. The master receives a data byte.
5. The master asserts NO ACK on SDA.
6. The master asserts a stop condition on SDA, and the
transaction ends.
In the ADT7490, 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 write byte operation. This operation
is illustrated in Figure 24.
1
2
34
56
S
SLAVE
ADDRESS
R
A
DATA
AP
Figure 24. Single-Byte Read from a Register
Alert Response Address
Alert response address (ARA) is a feature of SMBus devices that
allows an interrupting device to identify itself to the host when
multiple devices exist on the same bus.
The SMBALERT output can be used as either an interrupt
output or an SMBALERT. One or more outputs can be
connected to a common SMBALERT line connected to the
master. If a device’s SMBALERT line goes low, the following
events occur:
1. SMBALERT is pulled low.
2. The master initiates a read operation and sends the alert
response address (ARA = 0001 100). This is a general call
address that 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 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 accor-
dance with normal SMBus arbitration.
5. Once the ADT7490 has responded to the alert response
address, the master must read the status registers, and the
SMBALERT is cleared only if the error condition is gone.
Rev. 0 | Page 15 of 76
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