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AD7292

Data Sheet

Rev. A | Page 18 of 40

SERIAL PORT INTERFACE (SPI)

The AD7292 serial port interface (SPI) allows the user to

configure the device for specific functions and operations

through an internal structured register space. The interface

consists of four signals: CS, SCLK, DIN, and DOUT. The SPI

reference level is set by Pin 5 (VDRIVE) to a level in the range of

1.8 V to 5.25 V.

SCLK is the serial clock input for the device; all data transfers

on DIN or DOUT take place with respect to SCLK. The chip

select input pin (CS) is an active low control that initiates the

data transfer and conversion process.

Data is clocked into the AD7292 on the SCLK falling edge.

Data is loaded into the device MSB first. The length of each

frame can vary and depends on the command being sent. Data

is clocked out of the AD7292 on DOUT in the same frame as

the read command, on the rising edge of SCLK while CS is low.

When CS is high, the SCLK and DIN signals are ignored and

the DOUT line becomes high impedance.

INTERFACE PROTOCOL

When reading from or writing to the AD7292, the first byte con-

tains the address pointer (see Table 13). Bit D7 and Bit D6 of the

address pointer are the read and write bits, respectively. Bit D5 to

Bit D0 of the address pointer specify the register address for the

read or write operation. A register can be simultaneously read

from and written to by setting both Bit D7 and Bit D6 to 1.

Table 13. Address Pointer

After the address pointer, subsequent data for writing to the part

is supplied in bytes (see Figure 36). Some registers are located

within register banks and, therefore, require both a pointer address

and a subpointer address. The subpointer address is specified

in the first byte following the pointer address (see Figure 37).

Figure 36 through Figure 38 show the read and write data formats.

These figures show read operations; for a write to a register or

subregister, the write bit is set and the DOUT line remains high

impedance.

If neither the read nor write bit is set (Bit D7 and Bit D6 of the

address pointer are set to 0), the address pointer is updated but

no data is read or written. Note that writing this command also

reinitializes the ADC sequencer (see the ADC Conversion

Control section).

On completion of a read or write, the AD7292 is ready to accept

a new pointer address; alternatively, the CS pin can be taken high

to terminate the operation.

LSB

t11

t12

t10

HIGH-Z

BUSY2

SCLK

DIN

DOUT1

1PROVIDED THE READ BIT IS SET.

2IF AN ADC CONVERSION IS REQUESTED.

t7 = 5ns IF NO ADC CONVERSION

955ns WITH ADC CONVERSION

Figure 35. Serial Interface Timing Diagram

POINTER [D5:D0]

DIN [D15:D8]

DIN [D7:D0]

DIN

DOUT

DOUT [D15:D0]1

1PROVIDED THE READ BIT IS SET.

Figure 36. Accessing a 16-Bit Register

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