ADM1021A(2012) View Datasheet(PDF) - ON Semiconductor
Part Name
Description
Manufacturer
ADM1021A Datasheet PDF : 16 Pages
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ADM1021A
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SCLK
SDATA
A6
START BY
MASTER
A5 A4 A3 A2 A1 A0 R/W
D7
ACK. BY
FRAME 1
ADM1021A
SERIAL BUS ADDRESS BYTE
D6 D5 D4 D3 D2 D1 D0
ACK. BY
FRAME 2
ADM1021A
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 15. Writing to the Address Pointer Register Only
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91
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SCLK
SDATA
A6
START BY
MASTER
A5 A4 A3 A2 A1 A0 R/W
D7
ACK. BY
FRAME 1
ADM1021A
SERIAL BUS ADDRESS BYTE
D6 D5 D4 D3 D2 D1 D0
NO ACK. BY
FRAME 2
MASTER
DATA BYTE FROM ADM1021A
STOP BY
MASTER
Figure 16. Reading Data from a Previously Selected Register
When reading data from a register there are two
possibilities:
1. If the ADM1021A’s address pointer register value
is unknown or not the desired value, it is first
necessary to set it to the correct value before data
can be read from the desired data register. This is
done by performing a write to the ADM1021A as
before, but only the data byte containing the
register read address is sent, because data is not to
be written to the register. This is shown in
Figure 15.
A read operation is then performed consisting of
the serial bus address, R/W bit set to 1, followed
by the data byte read from the data register. This is
shown in Figure 16.
2. If the address pointer register is known to be
already at the desired address, data can be read
from the corresponding data register without first
writing to the address pointer register, so Figure 15
can be omitted.
NOTES:Although it is possible to read a data byte from a data
register without first writing to the address pointer register,
if the address pointer register is already at the correct value,
it is not possible to write data to a register without writing to
the address pointer register; this is because the first data
byte of a write is always written to the address pointer
register.
Remember that the ADM1021A registers have different
addresses for read and write operations. The write address
of a register must be written to the address pointer if data is
to be written to that register, but it is not possible to read data
from that address. The read address of a register must be
written to the address pointer before data can be read from
that register.
ALERT Output
The ALERT output goes low whenever an out-of-limit
measurement is detected, or if the remote temperature sensor
is open-circuit. It is an open drain and requires a 10 kW
pullup to VDD. Several ALERT outputs can be wire-ANDed
together so the common line goes low if one or more of the
ALERT outputs goes low.
The ALERT output can be used as an interrupt signal to a
processor, or it can be used as an SMBALERT. Slave devices
on the SMBus cannot normally signal to the master that they
want to talk, but the SMBALERT function allows them to do
so.
One or more ALERT outputs are connected to a common
SMBALERT line connected to the master. When the
SMBALERT line is pulled low by one of the devices, the
following procedure occurs, as shown in Figure 17.
MASTER RECEIVES SMBALERT
START
ALERT RESPONSE
ADDRESS
RD ACK
DEVICE
ADDRESS
NO
ACK
STOP
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
Figure 17. Use of SMBALERT
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 that must not be used as a
specific device address.
3. The device whose ALERT 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 ALERT output is low,
the one with the lowest device address has priority,
in accordance with normal SMBus arbitration.
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