AD779 Просмотр технического описания (PDF) - Analog Devices

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AD779

Complete Sampling ADC 14-Bit 128 kSPS

Analog Devices 

AD779

AD779 TO 80186

Figure 10 shows the AD779 interfaced to the 80186 micropro-

cessor. This interface allows the 80186’s built-in DMA control-

ler to transfer the AD779 output into a RAM based FIFO buffer

of any length, with no microprocessor intervention.

execution in one 80 ns cycle, the digital signal processor will

support the AD779 data memory interface with two wait states.

The converter runs asychronously using a sampling clock. The

EOC output to the AD779 gets asserted at the end of each

conversion and causes an interrupt. Upon interrupt, the ADSP-

2100A starts a data memory read by providing an address on

the DMA bus. The decoded address generates OE for the

converter. OE, together with logic and latch, is used to force the

ADSP-2100A into a one cycle wait state by generating

DMACK. The read operation is thus started and completed

within two processor cycles (160 ns).

Figure 10. AD779 to 80186 DMA Interface

AD779 TO Z80

The AD779 can be interfaced to the Z80 processor in an I/O or

memory mapped configuration. Figure 11 illustrates an I/O con-

figuration, where the AD779 occupies several port addresses to

allow separate polling of the EOC status and reading of the data.

Figure 12. AD779 to ADSP-2100A Interface

Figure 11. AD779 to Z80 Interface

A useful feature of the Z80 is that a single wait state is automati-

cally inserted during I/O operations, allowing the AD779 to be

used with Z80 processors having clock speeds up to 8 MHz.

The AD779 is asynchronous which allows conversions to be ini-

tiated by an external trigger source independent of the micro-

processor clock. After each conversion, the AD779 EOC signal

generates a DMA request to Channel 1 (DRQ1). The subse-

quent DMA READ resets the interrupt latch. The system de-

signer must assign a sufficient priority to the DMA channel to

ensure that the DMA request will be serviced before the com-

pletion of the next conversion. This configuration can be used

with 6 MHz and 8 MHz 80186 processors.

Figure 13. Harmonic Distortion vs. Input Frequency

(0.5 dB Input)

AD779 TO ANALOG DEVICES ADSP-2100A

Figure 12 demonstrates the AD779 interfaced to an ADSP-

2100A. With a clock frequency of 12.5 MHz, and instruction

REV. B

Figure 14. Total Harmonic Distortion vs. Input Frequency

and Amplitude

–11–

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