AD7747

Rev. 0 | Page 15 of 28

STATUS REGISTER

Address Pointer 0x00, Read Only, Default Value 0x07

This register indicates the status of the converter. The status register can be read via the 2-wire serial interface to query a finished

conversion.

The RDY pin reflects the status of the RDY bit. Therefore, the RDY pin high-to-low transition can be used as an alternative indication of

the finished conversion.

Table 9. Status Register Bit Map

Bit

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Mnemonic

–

–

–

–

–

RDY

RDYVT

RDYCAP

Default

0

0

0

0

0

1

1

1

Table 10.

Bit

Mnemonic

Description

7 to 3

–

Not used, always read 0.

2

RDY

RDY = 0 indicates that conversion on the enabled channel(s) is complete and new unread data is available.

If both capacitive and voltage/temperature channels are enabled, the RDY bit is changed to 0 after conversion

on both channels is complete. The RDY bit returns to 1 either when data is read or prior to finishing the next

conversion. If, for example, only the capacitive channel is enabled, then the RDY bit reflects the RDYCAP bit.

1

RDYVT

RDYVT = 0 indicates that a conversion on the voltage/temperature channel is complete and new unread data

is available.

0

RDYCAP

RDYCAP = 0 indicates that a conversion on the capacitive channel is complete and new unread data is available.

CAP DATA REGISTER

24 Bits, Address Pointer 0x01, 0x02, 0x03, Read-Only,

Default Value 0x000000

This register contains the capacitive channel output data. The

register is updated after finished conversion on the capacitive

channel, with one exception: When the serial interface read

operation from the Cap Data register is in progress, the data

register is not updated and the new capacitance conversion

result is lost.

The stop condition on the serial interface is considered to be the

end of the read operation. Therefore, to prevent data corruption,

all three bytes of the data register should be read sequentially

using the register address pointer auto-increment feature of the

serial interface.

To prevent losing some of the results, the Cap Data register

should be read before the next conversion on the capacitive

channel is finished.

The 0x000000 code represents negative full scale (−8.192 pF),

the 0x800000 code represents zero scale (0 pF), and the

0xFFFFFF code represents positive full scale (+8.192 pF).

VT DATA REGISTER

24 Bits, Address Pointer 0x04, 0x05, 0x06, Read-Only,

Default Value 0x000000

This register contains the voltage/temperature channel output

data. The register is updated after finished conversion on the

voltage channel or temperature channel, with one exception:

When the serial interface read operation from the VT Data

register is in progress, the data register is not updated and the

new voltage/temperature conversion result is lost.

The stop condition on the serial interface is considered to be the

end of the read operation. Therefore, to prevent data corruption,

all three bytes of the data register should be read sequentially

using the register address pointer auto-increment feature of the

serial interface.

the 0x800000 code represents zero scale (0 V), and the

To prevent losing some of the results, the VT Data register

should be read before the next conversion on the voltage/

temperature channel is complete.

For the temperature sensor, the temperature can be calculated

from code using the following equation:

Temperature (°C) = (Code/2048) − 4096