NCT214MT3R2G【PDF 14/19 页】IC TEMP SENSOR LOC/REM 10WDFN

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NCT214

http://onsemi.com

Figure 17. Reading Data from a Previously Selected Register

SCLK

SDATA

A5 A4 A3 A2 A1 A0

D5 D4 D3 D2 D1 D0

ACK. BY

NCT214

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

NCT214

R/W

When reading data from a register there are two

possibilities.

" If the address pointer register value of the NCT214 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 writing to the

NCT214 as before, but only the data byte containing

the register read address is sent, because data is not to

be written to the register see Figure 16.

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 see Figure 17.

" If the address pointer register is known to be at the

desired address, data can be read from the

corresponding data register without first writing to the

address pointer register and the bus transaction shown

in Figure 16 can be omitted.

NOTES:It is possible to read a data byte from a data register without

first writing to the address pointer register. However, 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.

Some of the 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

address. The read address of a register must be written to

the address pointer before data can be read from that

ALERT

Output

This is applicable when Pin 6 is configured as an 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 output

and requires a pullup resistor. Several ALERT

outputs can

be wire-ORed together, so that 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 as an SMBALERT

. Slave devices on the SMBus

cannot normally signal to the bus master that they want to

talk, but the SMBALERT

function allows them to do so.

One or more ALERT

outputs can be connected to a

common SMBALERT

line that is connected to the master.

When the SMBALERT

line is pulled low by one of the

devices, the following procedure occurs (see Figure 18):

Figure 18. Use of SMBALERT

ALERT RESPONSE

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

START

ACK

DEVICE

ADDRESS

ACK

STOP

MASTER RECEIVES 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. As the device address is seven

bits, an LSB of 1 is added. The address of the

device is now known and it can be interrogated in

the usual way.

4. If more than one devices ALERT

output is low,

the one with the lowest device address takes

priority, in accordance with normal SMBus

arbitration.

Once the NCT214 has responded to the alert response

address, it resets its ALERT

output, provided that the error

condition that caused the ALERT

no longer exists. If the

SMBALERT

line remains low, the master sends the ARA

again, and so on until all devices whose ALERT

outputs

were low have responded.

Low Power Standby Mode

The NCT214 can be put into low power standby mode by

setting Bit 6 of the configuration register. When Bit 6 is low,

the NCT214 operates normally. When Bit 6 is high, the

ADC is inhibited, and any conversion in progress is

terminated without writing the result to the corresponding

value register. However, the SMBus is still enabled. Power

consumption in the standby mode is reduced to 5 mA if there

is no SMBus activity, or 30 mA if there are clock and data

signals on the bus.

When the device is in standby mode, it is possible to

initiate a one-shot conversion of both channels by writing to

the one-shot register (Address 0x0F), after which the device

returns to standby. It does not matter what is written to the

one-shot register, all data written to it is ignored. It is also

possible to write new values to the limit register while in

standby mode. If the values stored in the temperature value

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