
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
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 th
e 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