Serial Port To Adc Interface - Analog Devices adsp-2100 Manual

13 Hardware Examples
13.5
An ADC (analog-to-digital converter) converts an analog signal to digital
samples that a DSP processor can operate on. The ADSP-21xx processors
can receive data from an ADC directly through a serial port.
Analog Devices' AD7872 is an ADC that requires no extra logic to
interface to the SPORT. The AD7872 converts an analog signal to 14-bit
samples. Each sample is padded with two zero MSBs to yield 16-bit
samples. The AD7872 outputs each sample serially, MSB first. Its digital
interface consists of three pins: SDATA, the serial data output; SCLK, for
clocking data out; and
word.
The serial port connection to the AD7872 is shown in Figure 13.6. The
timer regulates sampling via the
Instead of the timer, an unused serial clock or flag output from the ADSP-
21xx processor can be programmed to generate the
AD7872 generates SCLK internally and provides it to the processor. With
the CONTROL input held at –5 V, the SCLK signal is continuous, running
even when no data is being output.
Figure 13.6 Serial Port Interface To AD7872 ADC
Serial data is output from the SDATA output of the ADC to the
processor's DR pin. The
processor.
processor. Figure 13.7 shows the timing of the serial data transfer.
13 – 10

SERIAL PORT TO ADC INTERFACE

SSTRB
ADSP-21xx
RFS
SPORT
DR
SCLK
SSTRB
SSTRB
goes low when the first bit is transmitted to the
, (serial strobe), which frames each serial
CONVST
input at a constant frequency.
+5 V
4.7 kΩ 2 kΩ 4.7 kΩ
SSTRB
SDATA
SCLK
signal provides the RFS input to the
CONVST
signal. The
AD7872 TIMER
CONVST
CONTROL –5 V