AD7918_15 datasheet(24/28 Pages) AD

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AD7908/AD7918/AD7928

Data Sheet

Rev. E | Page 24 of 28

The AD7908 outputs a leading zero and three channel address

bits that the conversion result corresponds to, followed by the

8-bit conversion result and four trailing zeros. The AD7918

outputs a leading zero and three channel address bits that the

conversion result corresponds to, followed by the 10-bit

conversion result and two trailing zeros. The 16-bit word read

from the AD7928 always contains a leading zero and three

channel address bits that the conversion result corresponds to,

followed by the 12-bit conversion result.

MICROPROCESSOR INTERFACING

The serial interface on the AD7908/AD7918/AD7928 allows the

part to be directly connected to a range of many different

microprocessors. This section explains how to interface the

AD7908/AD7918/AD7928 with some of the more common

microcontroller and DSP serial interface protocols.

AD7908/AD7918/AD7928 to TMS320C541

The serial interface on the TMS320C541 uses a continuous

serial clock and frame synchronization signals to synchronize

the data transfer operations with peripheral devices like the

AD7908/AD7918/AD7928. The CS input allows easy interfacing

between the TMS320C541 and the AD7908/AD7918/AD7928

without any glue logic required. The serial port of the

TMS320C541 is set up to operate in burst mode with internal

CLKX0 (Tx serial clock on Serial Port 0) and FSX0 (Tx frame

sync from Serial Port 0). The serial port control register (SPC)

must have the following setup: FO = 0, FSM = 1, MCM = 1, and

TXM = 1. The connection diagram is shown in Figure 26. It

should be noted that for signal processing applications, it is

imperative that the frame synchronization signal from the

TMS320C541 provides equidistant sampling. The VDRIVE pin of

the AD7908/AD7918/AD7928 takes the same supply voltage as

that of the TMS320C541. This allows the ADC to operate at a

higher voltage than the serial interface, that is, TMS320C541, if

necessary.

TMS320C5411

AD7908/

AD7918/

AD79281

CLKX

CLKR

FSX

FSR

VDD

SCLK

DOUT

DIN

1ADDITIONAL PINS REMOVED FOR CLARITY.

VDRIVE

Figure 26. Interfacing to the TMS320C541

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