AD7846AP datasheet(16/24 Pages) AD

16 / 24 page

AD7846

Rev. G | Page 16 of 24

MICROPROCESSOR INTERFACING

AD7846-TO-8086 INTERFACE

Figure 26 shows the 8086 16-bit processor interfacing to the

AD7846. The double buffering feature of the DAC is not used in

this circuit because LDAC is permanently tied to 0 V. AD0 to

AD15 (the 16-bit data bus) are connected to the DAC data bus

(DB0 to DB15). The 16-bit word is written to the DAC in one

MOV instruction and the analog output responds immediately.

In this example, the DAC address is 0xD000.

AD7846*

+5V

DATA BUS

LDAC

CLR

R/W

DB0 TO DB15

16-BIT

LATCH

8086

ALE

DEN

AD0 TO AD15

ADDRESS

DECODE

ADDRESS BUS

*LINEAR CIRCUITRY OMITTED FOR CLARITY

Figure 26. AD7846-to-8086 Interface Circuit

In a multiple DAC system, the double buffering of the AD7846

allows the user to simultaneously update all DACs. In Figure 27,

a 16-bit word is loaded to the input latches of each of the DACs

in sequence. Then, with one instruction to the appropriate

address, CS4 (that is, LDAC) is brought low, updating all the

DACs simultaneously.

+5V

DATA BUS

*LINEAR CIRCUITRY OMITTED FOR CLARITY

16-BIT

LATCH

ADDRESS

DECODE

ADDRESS BUS

AD7846*

LDAC

R/W

DB0 TO DB15

8086

ALE

DEN

AD0 TO AD15

CLR

+5V

CLR

+5V

AD7846*

LDAC

R/W

DB0 TO DB15

AD7846*

LDAC

R/W

DB0 TO DB15

Figure 27. AD7846-to-8086 Interface: Multiple DAC System

AD7846-TO-MC68000 INTERFACE

Interfacing between the AD7846 and MC68000 is accomplished

using the circuit of Figure 28. The following routine writes data

to the DAC latches and then outputs the data via the DAC latch.

1000

MOVE.W

#W,

The desired DAC data,

W, is loaded into

Data Register 0. W

may be any value

between 0 and 65535

(decimal) or 0 and

FFFF (hexadecimal).

MOVE.W

D0,

$E000

The data, W, is

transferred between

D0 and the DAC

MOVE.W

TRAP

#228,

#14

Control is returned

to the System Monitor

using these two

instructions.

AD7846*

+5V

DATA BUS

LDAC

CLR

R/W

MC68000

DTACK

R/W

A1 TO A23

ADDRESS

DECODE

ADDRESS BUS

D0 TO D15

DB0 TO DB15

*LINEAR CIRCUITRY OMITTED FOR CLARITY

Figure 28. AD7846-to-MC68000 Interface

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