Datasheet

AD7621
Rev. 0 | Page 26 of 32
MICROPROCESSOR INTERFACING
The AD7621 is ideally suited for traditional dc measurement
applications supporting a microprocessor, and ac signal
processing applications interfacing to a digital signal processor.
The AD7621 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 AD7621 to prevent digital noise from coupling
into the ADC. The following section illustrates the use of the
AD7621 with an ADSP-219x SPI-equipped DSP.
SPI Interface (ADSP-219x)
Figure 42 shows an interface diagram between the AD7621 and
an SPI-equipped DSP, ADSP-219x. To accommodate the slower
speed of the DSP, the AD7621 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.
04565-045
BUSY
CS
SDOUT
SCLK
CNVST
AD7621*
PFx
SPIxSEL (PFx)
MISOx
SCKx
PFx OR TFSx
ADSP-219x*
*ADDITIONAL PINS OMITTED FOR CLARITY
DVDD
SER/PAR
EXT/INT
RD
INVSCLK
Figure 42. Interfacing the AD7621 to SPI Interface