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AD574A

Complete 12-Bit A/D Converter

Analog Devices 

Figure 15. Z80—AD574A Interface

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 VLOGIC 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 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

REV. B

–11–

Figure 19. 68000—AD574A Interface

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