ad7886kp Analog Devices, Inc., ad7886kp Datasheet - Page 10

• Manufacturer Part Number: ad7886kp
• Description: Lc2mos 12-bit, 750 Khz/1 Mhz, Sampling Adc
• Manufacturer: Analog Devices, Inc.

AD7886
determined by the largest harmonic in the spectrum, but for
parts where the harmonics are buried in the noise floor, the peak
will be a noise peak.
MICROPROCESSOR INTERFACING
The AD7886 is designed to interface to microprocessors as a
memory mapped device. Its CS and RD control inputs are com-
mon to all memory peripheral interfacing. Figures 15 to 21
demonstrate typical interfaces for the AD7886.
AD7886–TMS320C10/TMS32020
Figures 15 and 16 show typical interfaces for the TMS320C10
and the TMS32020 DSP processors. An external timer controls
conversion start to the processor. At the end of each conversion,
the ADC’s BUSY output interrupts the microprocessor. The
conversion result can then be read from the ADC with the fol-
lowing instruction:
AD788S ADSP-2100/TMS320C25/DSP56000
Some of the faster DSP processors have data access times out-
side the capabilities of the AD7886. Interfacing to such proces-
sors requires the use of either a single WAIT state or external
latches. Examples are shown in Figures 17, 18 and 19.
The use of a single WAIT state for the TMS320C25 and the
ADSP-2100 interfaces extends the read instruction to the ADC
by one processor CLK OUT cycle. In the DSP56000 example,
the ADC’s data is first clocked into 74HC374 latches before be-
ing read by the processor. The AD7886’s CS and RD inputs are
tied permanently low, and the rising edge of BUSY updates the
latches at the end of conversion. Both methods of overcoming
the very fast data access time required by these processors are
interchangeable, i.e., a WAIT state can be used for the DSP56000,
eliminating the need for latches or vice or versa, for the other
two interfaces.
For all three interfaces, an external timer controls conversion
start; the processor is interrupted at the end of each conversion
by the ADC’s BUSY output. The following instruction then
reads data from the ADC:
IN D,ADC (ADC = ADC address)
ADSP-2100 – MR = DM(ADC)
TMS320C25 – IN D,ADC
DSP56000 – MOVEP Y:ADC,XO
Assuming the ADC is memory mapped into the top
64 locations in Y memory space. (ADC = ADC address)
Figure 14. AD7886 IMD Plot
–10–
TMS320C10
TMS32020
Figure 15. AD7886-TMS320C10 Interface
Figure 16. AD7886-TMS32020 Interface
STRB
MEN
INTn
DEN
PA2
PA0
R/W
D15
A15
D15
INT
D0
A0
D0
IS
*ADDITIONAL PINS OMITTED FOR CLARITY
*ADDITIONAL PINS OMITTED FOR CLARITY
ADDRESS BUS
ADDRESS BUS
EN
ENCODE
EN
ENCODE
ADDR
ADDR
DATA BUS
DATA BUS
TIMER
TIMER
BUSY
RD
DB11
DB0
CONVST
CS
CONVST
CS
BUSY
RD
DB11
DB0
AD7886*
AD7886*
REV. B