ADM1177

Preliminary Technical Data

Rev. PrD | Page 12 of 16

WRITE AND READ OPERATIONS

types of read and write operations. The ones used in the

ADM1177 are discussed below. The following abbreviations are

used in the diagrams:

S

START

P

STOP

R

READ

W

WRITE

A

ACKNOWLEDGE

N

NO ACKNOWLEDGE

QUICK COMMAND

This operation allows the master check if the slave is present on

the bus. This entails the following:

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 ACK on SDA.

S

SLAVE

ADDRESS

WA

12

3

Figure 9. Quick Command

WRITE COMMAND BYTE

In this 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 ACK 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 next section.)

5.

The slave asserts ACK on SDA.

6.

The master asserts a STOP condition on SDA to end the

transaction.

S

SLAVE

ADDRESS

WA

A

COMMAND

BYTE

P

12

3

4

56

Figure 10. Command Byte Write

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

control the ADM1177. Details of the function of each bit are

provided in Table 6.

Table 6. Command Byte Operations

Bit

Default

Name

Function

C0

0

V_CONT

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

ADM1177 will ACK and return all zeros in the returned data.

C1

0

V_ONCE

C2

0

I_CONT

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

ADM1177 will ACK and return all zeros in the returned data.

C3

0

I_ONCE

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 26.63 V for VRANGE = 0 and 6.66 V for VRANGE = 1.

C5

0

N/A

Unused

C6

0

STATUS_RD

Status Read. When this bit is set the data byte read back from the ADM1177 will be the STATUS byte. This

contains the status of the device alerts. See Table14 for full details of the status byte.