ADM1178 Просмотр технического описания (PDF) - Analog Devices

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ADM1178

Hot Swap Controller and Digital Power Monitor with ALERTB Output

Analog Devices 

Data Sheet

WRITE AND READ OPERATIONS

The I2C specification defines several protocols for different types of

read and write operations. The operations used in the ADM1178

are discussed in this section. Table 6 shows the abbreviations

used in the command diagrams (see Figure 38 to Figure 43).

Table 6. I2C Abbreviations

Abbreviation

S

P

R

W

A

N

Condition

Start

Stop

Read

Write

Acknowledge

No acknowledge

QUICK COMMAND

The quick command operation allows the master to check if the

slave is present on the bus, 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 acknowledge on SDA.

4. The master asserts a stop condition on SDA to end the

transaction.

1

2

34

S

SLAVE

ADDRESS

WA

P

Figure 38. Quick Command

ADM1178

WRITE COMMAND BYTE

In the write command byte operation, the master device sends

a command byte to the slave device, 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 acknowledge on SDA.

4. The master sends the command byte. The command byte is

identified by an MSB = 0. An MSB = 1 indicates an extended

register write (see the Write Extended Command Byte

section).

5. The slave asserts an acknowledge on SDA.

6. The master asserts a stop condition on SDA to end the

transaction.

1

2

3

4

56

S

SLAVE

ADDRESS

WA

COMMAND

BYTE

A

P

Figure 39. Write Command Byte

The seven LSBs of the command byte are used to configure and

control the ADM1178. Table 7 provides details of the function

of each bit.

Table 7. Command Byte Operations

Bit Default Name

Function

C0 0

V_CONT

LSB, set to convert voltage continuously. If readback is attempted before the first conversion is complete,

the ADM1178 asserts an acknowledge and returns all 0s in the returned data.

C1 0

V_ONCE

Set to convert voltage once. Self-clears. I2C asserts a no acknowledge on attempted reads until the ADC

conversion is complete.

C2 0

I_CONT

Set to convert current continuously. If readback is attempted before the first conversion is complete, the

ADM1178 asserts an acknowledge and returns all 0s in the returned data.

C3 0

I_ONCE

Set to convert current once. Self-clears. I2C asserts a no acknowledge on attempted reads until the ADC

conversion is complete.

C4 0

VRANGE

Selects different internal attenuation resistor networks for voltage readback. A 0 in C4 selects a 14:1

voltage divider. A 1 in C4 selects a 7:2 voltage divider. With an ADC full scale of 1.902 V, the voltage at the

VCC pin for an ADC full-scale result is 26.35 V for VRANGE = 0 and 6.65 V for VRANGE = 1.

C5 0

Not applicable Unused.

C6 0

STATUS_RD

Status read. When this bit is set, the data byte read back from the ADM1178 is the status byte. This

contains the status of the device alerts. See Table 15 for full details of the status byte.

Rev. D | Page 17 of 24

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