REV. 0

AD7719

–19–

Communications Register (A3, A2, A1, A0 = 0, 0, 0, 0)

The Communications Register is an 8-bit write-only register. All communications to the part must start with a write operation to the

Communications Register. The data written to the Communications Register determines whether the next operation is a read

or write operation, and to which register this operation takes place. For read or write operations, once the subsequent read or write

operation to the selected register is complete, the interface returns to where it expects a write operation to the Communications

Register. This is the default state of the interface, and on power-up or after a RESET, the AD7719 is in this default state waiting for

a write operation to the Communications Register. In situations where the interface sequence is lost, a write operation of at least 32

serial clock cycles with DIN high, returns the AD7719 to this default state by resetting the part. Table IX outlines the bit designa-

tions for the Communications Register. CR0 through CR7 indicate the bit location, CR denoting the bits are in the Communications

Register. CR7 denotes the first bit of the data stream.

CR7

CR6

CR5

CR4

CR3

CR2

CR1

CR0

WEN (0)

R/W (0)

0 (0)

0 (0)

A3 (0)

A2 (0)

A1 (0)

A0 (0)

Table IX. Communications Register Bit Designations

Bit

Bit

Location

Name

Description

CR7

WEN

Write Enable Bit. A 0 must be written to this bit so the write operation to the Communications Register

actually takes place. If a 1 is written to this bit, the part will not clock on to subsequent bits in the regis-

ter. It will stay at this bit location until a 0 is written to this bit. Once a 0 is written to the

WEN bit, the

next seven bits will be loaded to the Communications Register.

CR6

R/

W

A zero in this bit location indicates that the next operation will be a write to a specified register. A one in

this position indicates that the next operation will be a read from the designated register.

CR5

Zero

A zero must be written to this bit position to ensure correct operation of the AD7719.

CR4

Zero

A zero must be written to this bit position to ensure correct operation of the AD7719.

CR3–CR0

A3–A0

Register Address Bits. These address bits are used to select which of the AD7719’s registers are being

accessed during this serial interface communication. A3 is the MSB of the three selection bits.

Table X. Register Selection Table

A3

A2

A1

A0

Register

0000Communications Register during a Write Operation

0000

Status Register during a Read Operation

0001Mode Register

0010Main ADC Control Register (AD0CON)

0011Aux ADC Control Register (AD1CON)

0100Filter Register

0101Main ADC Data Register

0110Aux ADC Data Register

0111I/O Control Register

1000Main ADC Offset Calibration Register

1001Aux ADC Offset Calibration Register

1010Main ADC Gain Calibration Register

1011Aux ADC Gain Calibration Register

1100Test 1 Register

1101Test 2 Register

1110Undefined

1111ID Register