ADT7462ACPZ-R7 datasheet(18/81 Pages) ONSEMI

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ADT7462

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the #Bytes bits in the Configuration 0 register. The block

read operation consists of a send byte operation that sends

a block read command to the slave, immediately followed by

a repeated start and a read operation that reads out multiple

data bytes, 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 an ACK on SDA.

4. The master sends a command code that tells the slave

device to expect a block read. The ADT7462

command code for a block read is 0xA1 (1010 0001).

5. The slave asserts an ACK on SDA.

6. The master asserts a repeat start condition on SDA.

7. The master sends the 7−bit slave address followed

by the read bit (high).

8. The slave asserts an ACK on SDA.

9. The ADT7462 sends a byte count telling the

master how many data bytes to expect. The

maximum number of bytes is 32.

10. The master asserts an ACK on SDA.

11. The master receives the expected number of data

bytes.

12. The master asserts an ACK on SDA after each

data byte.

13. The ADT7462 issues a PEC byte to the master.

The master should check the PEC byte and issue

another block read if the PEC byte is incorrect.

14. A NO ACK is generated after the PEC byte to

signal the end of the read.

15. The master asserts a stop condition on SDA to end

the transaction.

Figure 31. Block Read from RAM

SLAVE

ADDRESS WA

COMMAND

0xA1 BLOCK

READ

DATA

PEC

BYTE

COUNT A DATA 1 A

SLAVE

ADDRESS

14 15

Note that although the ADT7462 supports packet error

checking (PEC), its use is optional. The PEC byte is

calculated using CRC−8. The frame check sequence (FCS)

conforms to CRC−8 by the polynomial.

C(x) + x8 ) x2 ) x1 ) 1

Consult the SMBus 1.1 specifications for more information.

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 procedure occurs:

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 ARA, 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 ADT7462 has responded to the ARA, the

master must read the status registers, and the

SMBALERT is cleared only if the error condition

has gone away.

SMBus Timeout

The ADT7462 includes an SMBus timeout feature. If

there is no SMBus activity for 25 ms, the ADT7462 assumes

that the bus is locked and releases the bus. This prevents the

device from locking or holding the SMBus while the device

is expecting data. Some SMBus controllers cannot handle

the SMBus timeout feature, so it can be disabled.

Configuration Register 3 (0x03)

Bit 1 SCL_Timeout = 1; SCL timeout enabled.

Bit 1 SCL_Timeout = 0; SCL timeout disabled (default).

Bit 2 SDA_Timeout = 1; SDA timeout enabled.

Bit 2 SDA_Timeout = 0; SDA timeout disabled (default).

Temperature and Voltage Measurement

Temperature Measurement

The ADT7462 can measure its own ambient temperature

and the temperature of up to three remote thermal diodes.

These diodes can be discrete diode−connected 2N3904/

2N3906s or they can be located on a processor die. Figure 32

shows how to connect a remote NPN or PNP transistor.

Figure 32. How to Measure Temperature Using

Discrete Transistors

D+

D–

ADT7462

2N3904

D+

D–

ADT7462

2N3906

Remote Thermal Diode 1 connects to Pin 15 and Pin 16.

Remote Thermal Diode 2 connects to Pin 17 and Pin 18.

Remote Thermal Diode 3 connects to Pin 19 and Pin 20.

A simple method of measuring temperature is to exploit

the negative temperature coefficient of a diode, measuring

the base−emitter voltage (VBE) of a transistor, operated at

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