Data Sheet

AD7787

Rev. A | Page 11 of 20

Table 6. Register Selection

RS1

RS0

Register

Register Size

0

0

Communications Register during a Write Operation

8-Bit

0

0

Status Register during a Read Operation

8-Bit

0

1

Mode Register

8-Bit

1

0

Filter Register

8-Bit

1

1

Data Register

24-Bit

Table 7. Channel Selection

CH1

CH0

Channel

0

0

AIN1(+) − AIN1(−)

0

1

AIN2

1

0

AIN1(−) − AIN1(−)

1

1

STATUS REGISTER (RS1, RS0 = 0, 0; POWER-ON/RESET = 0×8C)

The status register is an 8-bit read-only register. To access the ADC status register, the user must write to the communications register,

select the next operation to be a read, and load Bits RS1 and RS0 with 0s. Table 8 outlines the bit designations for the status register. SR0

through SR7 indicate the bit locations, SR denoting the bits are in the status register. SR7 denotes the first bit of the data stream. The

number in the parenthesis indicates the power-on/reset default status of that bit.

SR7

SR6

SR5

SR4

SR3

SR2

SR1

SR0

RDY (1)

ERR (0)

0 (0)

0 (0)

1 (1)

1 (1)

CH1 (0)

CH0 (0)

Table 8. Status Register Bit Designations

Bit

Location

Bit

Name

Description

SR7

RDY

Ready Bit for ADC. Cleared when data is written to the ADC data register. The RDY bit is set automatically after the

ADC data register has been read or a period of time before the data register is updated with a new conversion result

to indicate to the user not to read the conversion data. It is also set when the part is placed in power-down mode.

The end of a conversion is indicated by the DOUT/RDY pin also. This pin can be used as an alternative to the status

register for monitoring the ADC for conversion data.

SR6

ERR

ADC Error Bit. This bit is written to at the same time as the RDY bit. Set to indicate that the result written to the ADC

data register has been clamped to all 0s or all 1s. Error sources include overrange, underrange. Cleared by a write

operation to start a conversion.

SR5 to

SR4

0

These bits are automatically cleared.

SR3 to

SR2

1

These bits are automatically set.

SR1 to

SR0

CH1 to

CH0

These bits indicate which channel is being converted by the ADC.