AD7769
Conversion is initiated on the selected AD7769 ADC channel
using a single I/O instruction, <OUT ADC, A>. The processor
then polls
INT
until it goes low before reading the conversion
result using an <IN A, ADC> instruction. Writing data to the rel-
evant AD7769 DAC consists of an <OUT DAC, A> instruction.
AD7769–ADSP-2101 Interface
Figure 19 shows a typical interface to the DSP microcomputer,
the ADSP-2101. The ADSP-2101 is optimized for high speed
numeric processing tasks.
Figure 20. AD7769 to 8051 (Processor Bus) Interface
Figure 19. AD7769 to ADSP-2101 Interface
Because the instruction cycle of the ADSP-2101 is very fast
(80 ns cycle), the
WR
and
RD
pulses must be stretched out to
suit the AD7769. This is easily achieved as the ADSP-2101
memory interface supports slower memories and memory-
mapped peripherals (i.e., AD7769) with a programmable wait
state generation capability. A number of wait states, from 0 to 7,
can be specified for each memory interface. One wait state is
sufficient for the interface to the AD7769.
AD7769–8051 Interface
Figure 21. AD7769 to 8051 (Parallel l/O Ports) Interface
AD7769–MC68HC11 Interface
A choice of two interface modes are available to the 8051
microcomputer.
Figure 20 shows a typical interface to the 8051 processor bus. It
is suitable for the maximum 8051 clock frequency of 12 MHz.
In this interface mode, Port 0 provides the multiplexed low or-
der address and data bus and Port 2 provides the high order ad-
dress bus (A
8
–A
15
).
Figure 21 shows the AD7769 interfaced to the 8051 parallel I/O
ports. This interface circuit is simpler to implement than the
previous interface to the processor bus, but, in general, the
maximum data throughput rate is much slower (for the same
clock frequencies). In addition to its simplicity, the interface to
the parallel I/O ports versus the processor bus allows indepen-
dent control of both the
WR
and
RD
inputs to the AD7769.
For example, the 8051 can set both
WR
and
RD
low at the
same time. This permits data from the last ADC conversion to
be written directly from the ADC register into the selected DAC
register (see Logic Truth Table). This allows very fast transfer
of data from the ADC to the DAC and is a useful feature for
some applications such as a fast, programmable, infinite sample-
and-hold function.
Figure 22 shows a typical interface between the AD7769 and the
MC68HC11 microcomputer. This interface is designed for the
maximum MC68HC11 clock speed of 8.4 MHz. The microcom-
puter is operated in the expanded multiplexed mode, with the
AD7769 as a memory mapped peripheral. The expansion bus is
made up of Ports B and C, and control signals AS and R/W.
Figure 22. AD7769 to MC68HC11 Interfaced
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REV. A
AD [ ANALOG DEVICES ]
