AD7623AST datasheet(27/29 Pages) AD

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AD7623

Rev. 0 | Page 26 of 28

MICROPROCESSOR INTERFACING

The AD7623 is ideally suited for traditional dc measurement

applications supporting a microprocessor, and ac signal

processing applications interfacing to a digital signal processor.

The AD7623 is designed to interface with a parallel 8-bit or

16-bit wide interface, or with a general-purpose serial port or

I/O ports on a microcontroller. A variety of external buffers can

be used with the AD7623 to prevent digital noise from coupling

into the ADC. The SPI Interface (ADSP-219x) section shows

the use of the AD7623 with an ADSP-219x SPI-equipped DSP.

SPI Interface (ADSP-219x)

Figure 42 shows an interface diagram between the AD7623 and

an SPI-equipped DSP, ADSP-219x. To accommodate the slower

speed of the DSP, the AD7623 acts as a slave device, and data

must be read after conversion. This mode also allows the daisy-

chain feature. The convert command could be initiated in

response to an internal timer interrupt.

The reading process can be initiated in response to the end-of-

conversion signal (BUSY going low) using an interrupt line of

the DSP. The serial peripheral interface (SPI) on the ADSP-219x

is configured for master mode (MSTR) = 1, clock polarity bit

(CPOL) = 0, clock phase bit (CPHA) = 1, and SPI interrupt

enable (TIMOD) = 00 by writing to the SPI control register

(SPICLTx).

It should be noted that to meet all timing requirements, the SPI

clock should be limited to 17 Mb/s allowing it to read an ADC

result in less than 1 μs. When a higher sampling rate is desired,

use one of the parallel interface modes.

BUSY

SDOUT

SCLK

CNVST

AD7623*

PFx

SPIxSEL (PFx)

MISOx

SCKx

PFx OR TFSx

ADSP-219x*

*ADDITIONAL PINS OMITTED FOR CLARITY

DVDD

SER/PAR

EXT/INT

INVSCLK

Figure 42. Interfacing the AD7623 to SPI Interface

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