EVAL-AD7866CB AD [Analog Devices], EVAL-AD7866CB Datasheet - Page 18

• Manufacturer Part Number: EVAL-AD7866CB
• Description: Dual 1 MSPS, 12-Bit, 2-Channel SAR ADC with Serial Interface
• Manufacturer: AD [Analog Devices]

AD7866
Bit
15
14
13
12
D
Likewise, if CS is held low for a further 16 SCLK cycles on D
the data from conversion A will be output on D
trated in Figure 23 where the case for D
in this case the DOUT line in use will go back into three-state on
the 32nd SCLK rising edge or the rising edge of CS, whichever
occurs first.
Sixteen serial clock cycles are required to perform the conversion
process and to access data from one conversion on either data
line of the AD7866. CS going low provides the leading zero to
be read in by the microcontroller or DSP. The remaining data is
then clocked out by subsequent SCLK falling edges, beginning
with the first of three data STATUS bits, thus the first falling clock
edge on the serial clock has the leading zero provided and also
clocks out the first of three STATUS bits. The final bit in the
data transfer is valid on the 16th falling edge, having being clocked
out on the previous (15th) falling edge. In applications with a
slower SCLK, it is possible to read in data on each SCLK rising
edge, i.e., the first rising edge of SCLK after the CS falling edge
would have the leading zero provided and the 15th rising SCLK
edge would have DB0 provided.The three STATUS bits that
follow the leading zero provide information with respect to
the conversion result that follows them on the D
Table III shows how these identification bits can be interpreted.
MICROPROCESSOR INTERFACING
The serial interface on the AD7866 allows the parts to be directly
connected to a range of many different microprocessors. This
section explains how to interface the AD7866 with some of the
more common microcontroller and DSP serial interface protocols.
AD7866 to ADSP-218x
The ADSP-218x family of DSPs are directly interfaced to the
AD7866 without any glue logic required. The V
AD7866 takes the same supply voltage as that of the ADSP-218x.
This allows the ADC to operate at a higher supply voltage than
the serial interface, i.e., ADSP-218x, if necessary. This example
shows both D
both serial ports of the ADSP-218x.
OUT
A, the data from conversion B will be output on D
Bit Name
ZERO
RANGE
A0
A/B
OUT
A and D
OUT
B of the AD7866 connected to
Comment
Leading Zero. This bit will always be a zero output.
The polarity of this bit reflects the analog input range that has been selected with the RANGE
pin. If it is a 0, it means that in the previous transfer upon the falling edge of the CS, the range pin was
at a logic low providing an analog input range from 0 V to V
it means that in the previous transfer upon the falling edge of CS, the RANGE pin was at a logic high
resulting in an analog input range of 2 × V
This bit indicates on which channel the conversion is being performed, Channel 1 or Channel 2 of the
ADC in question. If this bit is a 0, the conversion result will be from Channel 1 of the ADC, and
if it is a 1, the result will be from Channel 2 of the ADC in question.
This bit indicates which ADC the conversion result is from. If this bit is a 0, the result is from ADC A;
and if it is a 1, the result is from ADC B. This is especially useful if only one serial port is available
for use and one D
OUT
A is shown. Note that
OUT
DRIVE
Table III. STATUS Bit Description
OUT
OUT
B. This is illus-
line is used, as shown in Figure 23.
line in use.
pin of the
OUT
OUT
A.
B,
The SPORT0 control register should be set up as follows:
The SPORT1 control register should be set up as follows:
To implement the power-down modes on the AD7866 SLEN
should be set to 1001 to issue an 8-bit SCLK burst. The con-
nection diagram is shown in Figure 24. The ADSP-218x has the
TFS0 and RFS0 of the SPORT0 and the RFS1 of SPORT1 tied
together, with TFS0 set as an output and both RFS0 and RFS1
set as inputs. The DSP operates in Alternate Framing Mode
and the SPORT control register is set up as described. The Frame
synchronization signal generated on the TFS is tied to CS and
as with all signal processing applications equidistant sampling is
necessary. However, in this example, the timer interrupt is used
to control the sampling rate of the ADC and under certain con-
ditions, equidistant sampling may not be achieved.
The Timer and other registers are loaded with a value that
will provide an interrupt at the required sample interval. When
an interrupt is received, a value is transmitted with TFS/DT
(ADC control word). The TFS is used to control the RFS and
hence the reading of data. The frequency of the serial clock is set
in the SCLKDIV register. When the instruction to transmit with
TFS is given, (i.e., AX0 = TX0), the state of the SCLK is checked.
The DSP will wait until the SCLK has gone High, Low, and
High before transmission will start. If the timer and SCLK values
are chosen such that the instruction to transmit occurs on or near
the rising edge of SCLK, the data may be transmitted or it may
wait until the next clock edge.
REF
TFSW = RFSW = 1, Alternate Framing
INVRFS = INVTFS = 1, Active Low Frame Signal
DTYPE = 00, Right Justify Data
SLEN = 1111, 16-Bit Data Words
ISCLK = 0, External Serial Clock
TFSR = RFSR = 1, Frame Every Word
IRFS = 0
ITFS = 1
TFSW = RFSW = 1, Alternate Framing
INVRFS = INVTFS = 1, Active Low Frame Signal
DTYPE = 00, Right Justify Data
SLEN = 1111, 16-Bit Data Words
ISCLK = 1, Internal Serial Clock
TFSR = RFSR = 1, Frame Every Word
IRFS = 0
ITFS = 1
selected for this conversion. See Analog Input section.
REF
for this conversion. If it is a 1,