AD7938/AD7939
Data Sheet
Rev. C | Page 30 of 36
AD7938/AD7939 to ADSP-21065L Interface
This interface is an example of one of three DMA handshake
modes. The MSX control line is actually three memory select
lines. Internal ADDR25-24are decoded into MS3to0, and these
lines are then asserted as chip selects. The DMAR1 (DMA
request 1) is used in this setup as the interrupt to signal the end
of conversion. The rest of the interface is a standard
handshaking operation.
AD7938/
AD7939*
ADSP-21065L*
WR
DB0 TO DB11
D0 TO D31
ADDR0 TO ADDR23
MSX
DMAR1
BUSY
CS
CONVST
DSP/USER SYSTEM
WR
RD
*ADDITIONAL PINS OMITTED FOR CLARITY.
ADDRESS BUS
DATA BUS
ADDRESS
LATCH
ADDRESS
DECODER
03715-
046
Figure 44. Interfacing to the ADSP-21065L
AD7938/AD7939 to TMS32020, TMS320C25, and
TMS320C5x Interface
Parallel interfaces between the AD7938/AD7939 and the
TMS32020, TMS320C25, and TMS320C5x family of DSPs are
the AD7938/AD7939 should be chosen to fall in the I/O
memory space of the DSPs. The parallel interface on the
AD7938/AD7939 is fast enough to interface to the TMS32020
with no extra wait states. If high speed glue logic, such as 74AS
devices, is used to drive the RD and the WR lines when
interfacing to the TMS320C25, no wait states are necessary.
However, if slower logic is used, data accesses can be slowed
sufficiently when reading from, and writing to, the part to
require the insertion of one wait state. Extra wait states are
necessary when using the TMS320C5x at their fastest clock
speeds (see the TMS320C5x User’s Guide for details).
Data is read from the ADC using the following instruction
IN D, ADC
where:
D is the data memory address.
ADC is the AD7938/AD7939 address.
AD7938/
AD7939*
TMS32020/
TMS320C25/
TMS320C50*
WR
RD
DB11 TO DB0
DMD0 TO DMD15
A0 TO A15
IS
READY
INTX
BUSY
CS
EN
CONVST
DSP/USER SYSTEM
TMS320C25
ONLY
R/W
STRB
*ADDITIONAL PINS OMITTED FOR CLARITY.
ADDRESS BUS
DATA BUS
ADDRESS
DECODER
03715-
047
MSC
Figure 45. Interfacing to the TMS32020/TMS320C25/TMS320C5x
AD7938/AD7939 to 80C186 Interface
Figure 46 shows the AD7938/AD7939 interfaced to the 80C186
microprocessor. The 80C186 DMA controller provides two
independent high speed DMA channels where data transfer can
occur between memory and I/O spaces. Each data transfer
consumes two bus cycles, one cycle to fetch data and the other
to store data. After the AD7938/AD7939 finish a conversion,
the BUSY line generates a DMA request to Channel 1 (DRQ1).
Because of the interrupt, the processor performs a DMA read
operation that also resets the interrupt latch. Sufficient priority
must be assigned to the DMA channel to ensure that the DMA
request is serviced before the completion of the next conversion.
AD7938/
AD7939*
80C186*
WR
DB0 TO DB11
AD0 TO AD15
A16 TO A19
ALE
DRQ1
BUSY
CS
Q
R
S
CONVST
MICROPROCESSOR/
USER SYSTEM
WR
RD
*ADDITIONAL PINS OMITTED FOR CLARITY.
ADDRESS/DATA BUS
ADDRESS BUS
DATA BUS
ADDRESS
LATCH
ADDRESS
DECODER
03715-
048
Figure 46. Interfacing to the 80C186