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.
For voltage input, Code 0 represents negative full scale (−V
REF
),
the 0x800000 code represents zero scale (0 V), and the
0xFFFFFF code represents positive full scale (+V
REF
).
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
