AD574A
Note: Due to the large number of options that may be installed
in the PC, the I/O bus loading should be limited to one Schottky
TTL load. Therefore, a buffer/driver should be used when inter-
facing more than two AD574As to the I/O bus.
8086 Interface
The data mode select pin (12/8) of the AD574A should be con-
nected to V
LOGIC
to provide a 12-bit data output. To prevent
possible bus contention, a demultiplexed and buffered address/
data bus is recommended. In the cases where the 8-bit short
conversion cycle is not used, A0 should be tied to digital com-
mon. Figure 18 shows a typical 8086 configuration.
Figure 15. Z80—AD574A Interface
Figure 16. Wait State Generator
IBM PC Interface
The AD574A appears in Figure 17 interfaced to the 4 MHz
8088 processor of an IBM PC. Since the device resides in I/O
space, its address is decoded from only the lower ten address
lines and must be gated with AEN (active low) to mask out in-
ternal DMA cycles which use the same I/O address space. This
active low signal is applied to
CS. IOR
and
IOW
are used to
initiate the conversion and read, and are gated together to drive
the chip enable, CE. Because the data bus width is limited to
8 bits, the AD574A data resides in two adjacent addresses
selected by A0.
Figure 18. 8086—AD574A with Buffered Bus lnterface
For clock speeds greater than 4 MHz wait state insertion similar
to Figure 16 is recommended to ensure sufficient CE and R/C
pulse duration.
The AD574A can also be interfaced in a stand-alone mode (see
Figure 13). A low going pulse derived from the 8086’s
WR
sig-
nal logically ORed with a low address decode starts the conver-
sion. At the end of the conversion, STS clocks the data into the
three-state latches.
68000 Interface
The AD574, when configured in the stand-alone mode, will eas-
ily interface to the 4 MHz version of the 68000 microprocessor.
The 68000 R/W signal combined with a low address decode ini-
tiates conversion. The
UDS
or
LDS
signal, with the decoded
address, generates the
DTACK
input to the processor, latching
in the AD574A’s data. Figure 19 illustrates this configuration.
Figure 17. IBM PC—AD574A Interface
Figure 19. 68000—AD574A Interface
REV. B
–11–
AD [ ANALOG DEVICES ]
