ADM1021AARQZ-R View Datasheet(PDF) - ON Semiconductor
Part Name
Description
Manufacturer
ADM1021AARQZ-R Datasheet PDF : 15 Pages
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ADM1021A
1
9
1
9
SCLK
SDATA
A6
START BY
MASTER
A5 A4 A3 A2 A1 A0
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
ACK. BY
ADM1021A
D6 D5 D4 D3 D2 D1 D0
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY STOP BY
ADM1021A MASTER
Figure 15. Writing to the Address Pointer Register Only
1
9
1
9
SCLK
SDATA
A6
START BY
MASTER
A5 A4 A3 A2 A1 A0
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
ACK. BY
ADM1021A
D6 D5 D4 D3 D2 D1 D0
NO ACK. STOP BY
BY MASTER MASTER
FRAME 2 DATA BYTE FROM ADM1021A
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:
1. 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.
2. 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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