AD7891 Datasheet, PDF (15/20 Pages) Analog Devices – LC2MOS 8-Channel, 12-Bit High Speed Data Acquisition System

AD7891
As in the 8X51 circuit above, the way that the 68HC11 is in-
formed that a conversion is completed is not shown in the dia-
gram. The EOC line can be used to inform the 68HC11 that a
conversion is complete by using it as an interrupt signal. The
interrupt service routine reads in the result of the conversion. If
a software conversion start is used, the 68HC11 can wait for
2.0 µs (AD7891-2) or 2.2 µs (AD7891-1) before reading from
the AD7891.
PC7
PC6
68HC11*
SCK
MOSI
MOSO
RFS
TFS
AD7891*
SCLK
DATA IN
DATA OUT
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 8. AD7891 to 68HC11 Interface
AD7891 to ADSP-21xx Serial Interface
An interface between the AD7891 and the ADSP-21xx is shown
in Figure 9. In the interface shown either SPORT0 or SPORT1
can be used to transfer data to the AD7891. When reading from
the part, the SPORT must be set up with a serial word length of
16 bits. When writing to the AD7891, a serial word length of 6
bits or more can be used. Other setups for the serial interface on
the ADSP-21xx internal SCLK, alternate framing mode and
active low framing signal. Normally the EOC line from the
AD7891 would be connected to the IRQ2 line of the ADSP-
21xx to interrupt the DSP at the end of a conversion (not shown
in diagram).
RFS
TFS
ADSP-21xx*
SCLK
DT
DR
RFS
TFS
AD7891*
SCLK
DATA IN
DATA OUT
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 9. AD7891 to ADSP-2101 Serial Interface
AD7891 to DSP5600x Serial Interface
Figure 10 shows a serial interface between the AD7891 and the
DSP5600x series of DSPs. When reading from the AD7891, the
DSP5600x should be set up for 16-bit data transfers, MSB first,
normal mode synchronous operation, internally generated word
frame sync and gated clock. When writing to the AD7891, 8-bit
or 16-bit data transfers can be used. The frame sync signal from
the DSP5600x must be inverted before being applied to the
RFS and TFS inputs of the AD7891 as shown in Figure 10.
To monitor the conversion time of the AD7891, a scheme such
as outlined in previous interfaces with EOC can be used. This
can be implemented by connecting the EOC line directly to the
IRQA input of the DSP5600x.
DSP56000/
DSP56002*
FST (SC2)
SCK
STD
SRD
RFS
TFS
AD7891*
SCLK
DATA IN
DATA OUT
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 10. AD7891 to DSP5600x Serial Interface
AD7891 to TMS320xxx Serial Interface
The AD7891 can be interfaced to the serial port of TMS320xxx
DSPs as shown in Figure 11. External timing generation cir-
cuitry is necessary to generate the serial clock and syncs neces-
sary for the interface.
TIMING
GENERATION
CIRCUITRY
TMS32020/ FSR
TMS320C25/
TMS320C5X/ FSX
TMS320C3X*
CLKR
CLKX
DX
RFS
TFS
AD7891*
SCLK
DATA IN
DR
DATA OUT
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 11. AD7891 to TMSxxx Serial Interface
REV. A
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