ADM1191

Rev. 0 | Page 13 of 16

READ VOLTAGE AND/OR CURRENT DATA BYTES

The ADM1191 can be set up to provide information in three

different ways (see the Write Command Byte section). Depending

on how the device is configured, the following data can be read

out of the device after a conversion (or conversions).

Voltage and Current Readback

The ADM1191 digitizes both voltage and current. Three bytes

are read out of the device in the format shown in Table 12.

Table 12. Voltage and Current Readback

Byte

Contents

B7

B6

B5

B4

B3

B2

B1

B0

1

Voltage

MSBs

V11

V10

V9

V8

V7

V6

V5

V4

2

Current

MSBs

I11

I10

I9

I8

I7

I6

I5

I4

3

LSBs

V3

V2

V1

V0

I3

I2

I1

I0

Voltage Readback

The ADM1191 digitizes voltage only. Two bytes are read out of

the device in the format shown in Table 13.

Table 13. Voltage Only Readback Format

Byte Contents

B7

B6

B5 B4 B3 B2

B1

B0

1

Voltage MSBs

V11

V10 V9

V8

V7

V6

V5

V4

2

Voltage LSBs

V3

V2

V1

V0

0

0

0

0

Current Readback

The ADM1191 digitizes current only. Two bytes are read out of

the device in the format shown in Table 14.

Table 14. Current Only Readback Format

Byte Contents

B7

B6

B5 B4 B3 B2

B1

B0

1

Current MSBs

I11

I10

I9

I8

I7

I6

I5

I4

2

Current LSBs

I3

I2

I1

I0

0

0

0

0

The following series of events occurs when the master receives

three bytes (voltage and current data) from the slave device:

1.

The master device asserts a start condition on SDA.

2.

The master sends the 7-bit slave address, followed by the

read bit (high).

3.

The addressed slave device asserts an acknowledge on SDA.

4.

The master receives the first data byte.

5.

The master asserts an acknowledge on SDA.

6.

The master receives the second data byte.

7.

The master asserts an acknowledge on SDA.

8.

The master receives the third data byte.

9.

The master asserts a no acknowledge on SDA.

10. The master asserts a stop condition on SDA, and the

transaction ends.

For cases where the master is reading voltage only or current

only, only two data bytes are read. Step 7 and Step 8 are not

required.

S

SLAVE

ADDRESS

RA DATA 1

DATA 2

NP

DATA 3

A

A

12

3

4

5

6

7

8

9 10

Figure 22. Three-Byte Read from ADM1191

S

SLAVE

ADDRESS

RA

REGISTER

ADDRESS

NP

REGISTER

DATA

A

12

3

4

5

6

7 8

Figure 23. Two-Byte Read from ADM1191

Converting ADC Codes to Voltage and Current Readings

The following equations can be used to convert ADC codes

representing voltage and current from the ADM1175 12-bit

ADC into actual voltage and current values.

where:

Code is the ADC voltage code read from the device (Bit V0

to Bit V11).

where:

Code is the ADC current code read from the device (Bit I0 to

Bit I11).

Read Status Register

A single register of status data can also be read from the

ADM1191.

1.

The master device asserts a start condition on SDA.

2.

The master sends the 7-bit slave address, followed by the

read bit (high).

3.

The addressed slave device asserts an acknowledge on SDA.

4.

The master receives the status byte.

5.

The master asserts an acknowledge on SDA.

S

SLAVE

ADDRESS

RA DATA 1 A

12

3

4

5

Figure 24. Status Read from ADM1191

Table 15 shows the ADM1191 status registers in detail. Note

that Bit 1, Bit 3, and Bit 5 are cleared by writing to Bit 4 of the

ALERT_EN register (CLEAR).