ADM1191

Rev. B | Page 13 of 16

READ VOLTAGE AND/OR CURRENT DATA BYTES

Depending on how the device is configured, ADM1191 can be

set up to provide information in three ways after a conversion

(or conversions): voltage and current readback, voltage only

readback, and current only readback. See the Write Command

Byte section for more details.

Voltage and Current Readback

The ADM1191 digitizes both voltage and current. Three bytes

are read back 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 back 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 back

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, two data bytes are read and 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

DATA 1

NP

DATA 2

A

12

3

4

5

6

7 8

Figure 23. Two-Byte Read from ADM1191

Converting ADC Codes to Voltage and Current Readings

Equation 1 and Equation 2 can be used to convert ADC codes

representing voltage and current from the ADM1191 12-bit ADC

into actual voltage and current values.

(1)

where:

Code is the ADC voltage code read from the device

(Bit V11 to Bit V0).

(2)

where:

Code is the ADC current code read from the device

(Bit I11 to Bit I0).

Read Status Register

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

ADM1191 as follows:

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

STATUS

BYTE

RA

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 (the

CLEAR bit) of the ALERT_EN register.