AD7891
PARALLEL INTERFACING
The parallel port on the AD7891 allows the device to be inter-
faced to microprocessors or DSP processors as a memory
mapped or I/O mapped device. The
CS
and
RD
inputs are
common to all memory peripheral interfacing. Typical interfaces
to different processors are shown in Figures 12 to 15. In all the
interfaces shown, an external timer controls the
CONVST
input
of the AD7891 and the
EOC
output interrupts the host DSP.
AD7891 to ADSP-21xx
Figure 12 shows the AD7891 interfaced to the ADSP-21xx
series of DSPs as a memory mapped device. A single wait state
may be necessary to interface the AD7891 to the ADSP-21xx
depending on the clock speed of the DSP. This wait state can be
programmed via the Data Memory Waitstate Control Register
of the ADSP-21xx (please see ADSP-2100 family Users manual
for details). The following instruction reads data from the
AD7891:
MR = DM(ADC)
where
ADC
is the address of the AD7891.
The parallel interface on the AD7891 is fast enough to interface
to the TMS32020 with no extra wait states. If high speed glue
logic such as 74AS devices are used to drive the
WR
and
RD
lines when interfacing to the TMS320C25, then again no wait
states are necessary. However, if slower logic is used, data ac-
cesses may be slowed sufficiently when reading from and writing
to the part to require the insertion of one wait state. In such a
case, this wait state can be generated using the single OR gate to
combine the
CS
and
MSC
signals to drive the READY line of
the TMS320C25, as shown in Figure 13. Extra wait states will
be necessary when using the TMS320C5x at their fastest clock
speeds. Wait states can be programmed via the IOWSR and
CWSR registers (please see TMS320C5x User Guide for details).
Data is read from the ADC using the following instruction:
IN D,ADC
where
D
is the memory location where the data is to be stored
and
ADC
is the I/O address of the AD7891.
AD7891 to TMS320C30
A13–A0
ADDRESS BUS
ADDR
DECODE
EN
CS
WR
RD
EOC
DATA BUS
DB11–DB0
ADSP-21xx*
DMS
WR
RD
IRQ2
D23–D8
Figure 14 shows a parallel interface between the AD7891 and
the TMS320C3x family of DSPs. The AD7891 is interfaced to
the Expansion Bus of the TMS320C3x. A single wait state is
required in this interface. This can be programmed using the
WTCNT bits of the Expansion Bus Control register (see
TMS320C3x Users guide for details). Data from the AD7891
can be read using the following instruction:
AD7891*
LDI *ARn,Rx
where
ARn
is an auxiliary register containing the lower 16 bits
of the address of the AD7891 in the TMS320C3x memory
space and
Rx
is the register into which the ADC data is loaded.
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 12. AD7891 to ADSP-21xx Parallel Interface
AD7891 to TMS32020, TMS320C25 and TMS320C5x
XA15–XA0
ADDRESS BUS
ADDR
DECODE
Parallel interfaces between the AD7891 and the TMS32020,
TMS320C25 and TMS320C5x family of DSPs are shown in
Figure 13. The memory mapped address chosen for the
AD7891 should be chosen to fall in the I/O memory space of
the DSPs.
TMS320C30*
IOSTRB
XR/W
CS
AD7891*
WR
RD
INTx
XD23–XD0
EXPANSION DATA BUS
EOC
DB11–DB0
A15–A0
ADDRESS BUS
*ADDITIONAL PINS OMITTED FOR CLARITY
ADDR
EN
DECODE
TMS320C25
ONLY
WR
RD
CS
TMS32020/
TMS320C25/
IS
TMS320C50*
READY
MSC
STRB
R/W
Figure 14. AD7891 to TMS320C30 Parallel Interface
AD7891*
INTx
D23–D0
DATA BUS
EOC
DB11–DB0
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 13. AD7891 to TMS32020/C25/C5x Parallel Interface
–16–
REV. A
AD [ ANALOG DEVICES ]
