AD7851

–12–

REV. B

STATUS REGISTER

The arrangement of the status register is shown below. The status register is a read-only register and contains 16 bits of data. The

status register is selected by first writing to the control register and putting two 1s in RDSLT1 and RDSLT0. The function of the

bits in the status register is described below. The power-up status of all bits is 0.

WRITE TO CONTROL REGISTER

SETTING RDSLT0 = RDSLT1 = 1

READ STATUS REGISTER

START

Figure 6. Flowchart for Reading the Status Register

MSB

ZERO

BUSY

ZERO

ZERO

ZERO

ZERO

PMGT1

PMGT0

RDSLT1

RDSLT0

2/3 MODE

X

CALMD

CALSLT1

CALSLT0

STCAL

LSB

Status Register Bit Function Descriptions

Bit No.

Mnemonic

Comment

15

ZERO

This bit is always 0.

14

BUSY

Conversion/Calibration Busy Bit. When this bit is 1, this indicates that there is a conversion or calibration

in progress. When this bit is 0, there is no conversion or calibration in progress.

13

ZERO

These four bits are always 0.

12

ZERO

11

ZERO

10

ZERO

9PMGT1

Power Management Bits. These bits along with the

SLEEP pin will indicate whether the part is in a power-

8PMGT0

down mode. (See Table VI in the Power-Down Options section for description.)

7

RDSLT1

Both these bits are always 1 indicating it is the status register that is being read. (See Table II.)

6

RDSLT0

52/

3 MODE

Interface Mode Select Bit. With this bit 0, the device is in Interface Mode 2. With this bit 1, the device is in

Interface Mode 1. This bit is reset to 0 after every read cycle.

4X

Don’t care bit.

3

CALMD

Calibration Mode Bit. A 0 in this bit indicates self-calibration is selected, and 1 in this bit indicates a system

calibration is selected (see Table III).

2

CALSLT1

Calibration Selection Bits and Start Calibration Bit. The STCAL bit is read as a 1 if a calibration is in

1

CALSLT0

progress and as a 0 if there is no calibration in progress. The CALSLT1 and CALSLT0 bits indicate which

0

STCAL

of the calibration registers are addressed for reading and writing (see the Calibration Registers section for

more details)