ADT7490(2016) 데이터 시트보기 (PDF) - ON Semiconductor
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ADT7490 Datasheet PDF : 75 Pages
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ADT7490
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 21.
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3
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S
SLAVE
ADDRESS
W
A
REGISTER
ADDRESS
AP
Figure 21. Setting a Register Address for
Subsequent Read
If the master is required to read data from the register
immediately 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 22.
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3
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5 6 78
S
SLAVE
ADDRESS
W
A
REGISTER
ADDRESS
A
DATA A P
Figure 22. Single-byte Write to a Register
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 23.
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2
3
S
SLAVE
ADDRESS
R
A
4
DATA
56
AP
Figure 23. 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 accordance 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.
SMBus Timeout
The ADT7490 includes an SMBus timeout feature. If
there is no SMBus activity for 35 ms, the ADT7490 assumes
the bus is locked and releases the bus. This prevents the
device from locking or holding the SMBus expecting data.
Some SMBus controllers cannot work with the SMBus
timeout feature, so it can be disabled.
Configuration Register 7 (Register 0x11)
Bit 4 (TODIS) = 0, SMBus Timeout Enabled (Default)
Bit 4 (TODIS) = 1, SMBus Timeout Disabled
Voltage Measurement Input
The ADT7490 has six external voltage measurement
channels. It can also measure its own supply voltage, VCC.
Pin 20 to Pin 23 can measure 5.0 V, 12 V, and 2.5 V
supplies, and the processor core voltage VCCP (0 V to 3.0 V
input). The 2.5 V input can be used to monitor a chipset
supply voltage in computer systems. The VCC supply
voltage measurement is carried out through the VCC pin
(Pin 4). Pin 8 measures the VTT voltage of the processor and
is the dedicated reference voltage for the PECI circuitry. The
IMON input on Pin 19 can be used to monitor the IMON
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