AD7875LPZ1 datasheet(19/28 Pages) AD

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AD7870/AD7875/AD7876

Rev. C | Page 19 of

MICROPROCESSOR INTERFACE

The AD7870/AD7875/AD7876 have a wide variety of

interfacing options. They offer two operating modes and

three data-output formats. Fast data access times allow

direct interfacing to most microprocessors including the

DSP processors.

PARALLEL READ INTERFACING

Figure 22, Figure 23, and Figure 24 show interfaces to the

ADSP-2100, TMS32010 and the TMS32020 DSP processors.

The ADC is operating in Mode 1, parallel read for all three

interfaces. An external timer controls conversion start asyn-

chronously to the microprocessor. At the end of each conversion

the ADC BUSY/INT interrupts the microprocessor. The

conversion result is read from the ADC with the following

instruction:

ADSP-2100: MR0 = DM(ADC)

TMS32010: IN D,ADC

TMS32020: IN D,ADC

MR0 = ADSP-2100 MR0 Register

D = Data Memory Address

ADC = AD7870/AD7875/AD7876 Address

Some applications may require that conversions be initiated by

the microprocessor rather than an external timer. One option

is to decode the CONVST signal from the address bus so that a

write operation to the ADC starts a conversion. Data is read at

the end of conversion as described earlier. Note: a read

operation must not be attempted during conversion.

DMA13

DMA0

CONVST

TIMER

12/8/CLK

BUSY/INT

DB11

DB0

1ADDITIONAL PINS OMITTED FOR CLARITY.

ADDRESS BUS

DATA BUS

ADDR

DECODE

DMS

IRQn

DMRD

DMD15

DMD0

AD7870/

AD7875/

AD78761

ADSP-2100

Figure 22. ADSP-2100 Parallel Interface

PA2

PA0

CONVST

TIMER

12/8/CLK

BUSY/INT

DB11

DB0

1ADDITIONAL PINS OMITTED FOR CLARITY.

ADDRESS BUS

DATA BUS

ADDR

DECODE

MEN

INT

DEN

D15

AD7870/

AD7875/

AD78761

TMS32010

Figure 23. TMS32010 Parallel Interface

A15

CONVST

TIMER

12/8/CLK

BUSY/INT

DB11

DB0

ADDRESS BUS

DATA BUS

ADDR

DECODE

INTn

STRB

D15

R/W

TMS32020

1ADDITIONAL PINS OMITTED FOR CLARITY.

AD7870/

AD7875/

AD78761

Figure 24. TMS32020 Parallel Interface

TWO-BYTE READ INTERFACING

68008 Interface

Figure 25 shows an 8-bit bus interface for the MC68008 micro-

processor. For this interface, the 12/8/CLK input is tied to 0 V

and the DB11/HBEN pin is driven from the microprocessor

least significant address bit. Conversion start control is provided

by the microprocessor. In this interface example, a Move instruc-

tion from the ADC address both starts a conversion and reads

the conversion result.

MOVEW ADC,DO

ADC = AD7870/AD7875/AD7876 address

D0 = 68008 D0 register

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