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ADM1025 Datasheet(PDF) 11 Page - ON Semiconductor

Part No. ADM1025
Description  Low Cost PC Hardware Monitor ASIC
Download  21 Pages
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com

ADM1025 Datasheet(HTML) 11 Page - ON Semiconductor

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Preliminary Technical Data
Rev. P5 | Page 11 of 21| www.onsemi.com
Figure 12. Writing to the Address Pointer Register Only
Figure 13. Reading Data from a Previously Selected Register
When reading data from a register there are two possibilities:
If the ADM1025/ADM1025A’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 ADM1025/ADM1025A as
before, but only the data byte containing the register
address is sent, since data should not be written to the
register. This is shown in Figure 12.
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 13.
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 12 can be omitted.
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 because
the first data byte of a write is always written to the
Address Pointer Register.
In Figure 11 to Figure 13, the serial bus address is shown as
the default value 01011(A1)(A0), where A1 and A0 are set
by the three-state ADD pin.
In addition to supporting the Send Byte and Receive Byte
protocols, the ADM1025/ADM1025A also supports the
Read Byte protocol (see System Management Bus
specifications Rev. 1.1 for more information).
If Reset or interrupt functionality is required, the address
pin cannot be strapped to GND, since this would keep the
ADD/RST/INT/NTO pin permanently low.
The ADM1025/ADM1025A has six external measurement
inputs, five for voltage and one (two pins) for temperature.
Internal measurements are also carried out on VCC and the on-
chip temperature sensor.
These inputs are multiplexed into the on-chip, successive-
approximation, analog-to-digital converter. This has a
resolution of eight bits. The basic input range is 0 V to 2.5 V, but
the inputs have built-in attenuators to allow measurement of
2.5 V, 3.3 V, 5 V, 12 V, and the processor core voltage VCCP
without any external components. To allow for the tolerance of
these supply voltages, the A/D converter produces an output of
¾ full scale (decimal 192) for the nominal input voltage and so
has adequate headroom to cope with overvoltages. Table 5
shows the input ranges of the analog inputs and output codes of
the A/D converter.
When the ADC is running, it samples and converts an input
every 11.6 ms, except for the external temperature (D+ and D−)
input. This has special input signal conditioning and is averaged
over 16 conversions to reduce noise; a measurement on this
input takes nominally 34.8 ms.

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