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ADM1021 Datasheet(PDF) 8 Page - Analog Devices

Part No. ADM1021
Description  Low Cost Microprocessor System Temperature Monitor
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADM1021 Datasheet(HTML) 8 Page - Analog Devices

 
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ADM1021
–8–
REV. 0
Table IV. Configuration Register Bit Assignments
Power-On
Bit
Name
Function
Default
7
MASK1
0 =
ALERT Enabled
0
1 =
ALERT Masked
6
RUN/STOP
0 = Run
0
1 = Standby
5-0
Reserved
0
Conversion Rate Register
The lowest three bits of this register are used to program the
conversion rate by dividing the ADC clock by 1, 2, 4, 8, 16, 32,
64 or 128, to give conversion times from 125 ms (Code 07h) to
16 seconds (Code 00h). This register can be written to and read
back over the SMBus. The higher five bits of this register are
unused and must be set to zero. Use of slower conversion times
greatly reduces the device power consumption, as shown in
Table V.
Table V. Conversion Rate Register Codes
Average Supply Current
Data
Conversion/sec
A Typ at VCC = 3.3 V
00h
0.0625
42
01h
0.125
42
02h
0.25
42
03h
0.5
48
04h
1
60
05h
2
82
06h
4
118
07h
8
170
08h to FFh
Reserved
Limit Registers
The ADM1021 has four limit registers to store local and re-
mote, high and low temperature limits. These registers can be
written to and read back, over the SMBus. The high limit regis-
ters perform a > comparison while the low limit registers per-
form a < comparison. For example, if the high limit register is
programmed as a limit of 80
°C, measuring 81°C will result in
an alarm condition.
One-Shot Register
The one-shot register is used to initiate a single conversion and
comparison cycle when the ADM1021 is in standby mode, after
which the device returns to standby. This is not a data register
as such and it is the write operation that causes the one-shot
conversion. The data written to this address is irrelevant and is
not stored.
SERIAL BUS INTERFACE
Control of the ADM1021 is carried out via the serial bus. The
ADM1021 is connected to this bus as a slave device, under the
control of a master device, e.g., the PIIX4.
ADDRESS PINS
In general, every SMBus device has a 7-bit device address
(except for some devices that have extended, 10-bit addresses).
When the master device sends a device address over the bus, the
slave device with that address will respond. The ADM1021 has
two address pins, ADD0 and ADD1, to allow selection of the
device address, so that several ADM1021s can be used on the
same bus, and/or to avoid conflict with other devices. Although
only two address pins are provided, these are three-state, and
can be grounded, left unconnected, or tied to VDD, so that a
total of nine different addresses are possible, as shown in Table VI.
It should be noted that the state of the address pins is only sampled
at power-up, so changing them after power-up will have no effect.
Table VI. Device Addresses
ADD0
ADD1
Device Address
0
0
0011 000
0
NC
0011 001
0
1
0011 010
NC
0
0101 001
NC
NC
0101 010
NC
1
0101 011
1
0
1001 100
1
NC
1001 101
1
1
1001 110
Note: ADD0, ADD1 sampled at power-up only.
The serial bus protocol operates as follows:
1. The master initiates data transfer by establishing a START
condition, defined as a high-to-low transition on the serial
data line SDATA, while the serial clock line SCLK remains
high. This indicates that an address/data stream will follow.
All slave peripherals connected to the serial bus respond to
the START condition and shift in the next eight bits, con-
sisting of a 7-bit address (MSB first) plus an R/
W bit, which
determines the direction of the data transfer, i.e., whether
data will be written to or read from the slave device.
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the Acknowl-
edge Bit. All other devices on the bus now remain idle while
the selected device waits for data to be read from or written
to it. If the R/
W bit is a 0, then the master will write to the
slave device. If the R/
W bit is a 1, the master will read from
the slave device.
2. Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an Acknowledge Bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, as a low-to-high transition
when the clock is high may be interpreted as a STOP signal.
The number of data bytes that can be transmitted over the
serial bus in a single READ or WRITE operation is limited
only by what the master and slave devices can handle.
3. When all data bytes have been read or written, stop condi-
tions are established. In WRITE mode, the master will pull
the data line high during the 10th clock pulse to assert a
STOP condition. In READ mode, the master device will
override the acknowledge bit by pulling the data line high
during the low period before the ninth clock pulse. This is
known as No Acknowledge. The master will then take the
data line low during the low period before the 10th clock
pulse, then high during the 10th clock pulse to assert a STOP
condition.


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