Preliminary Technical Data

AD7747

Rev. PrC| Page 13 of 20

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

7-3

-

Not used, always read 0.

2

RDY

RDY = 0 indicates that conversion on the enabled channel(s) has been finished 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 finished. 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 has been finished and new unread

data is available.

0

RDYCAP

RDYCAP = 0 indicates that a conversion on the capacitive channel has been finished and new unread data is

available.

CAP DATA REGISTER

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

Default Value 0x000000

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

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 finished.

For the temperature sensor, the temperature can be calculated

from code using the following equation:

Temperature (°C) = (Code/2048) − 4096