AD7845

REV. B

–10–

8-BIT MICROPROCESSOR SYSTEMS

Figure 22 shows an interface circuit for the AD7845 to the

8085A 8-bit microprocessor. The software routine to load data

to the device is given in Table IV. Note that the transfer of the

12 bits of data requires two write operations. The first of these

loads the 4 MSBs into the 7475 latch. The second write opera-

tion loads the 8 LSBs plus the 4 MSBs (which are held by the

latch) into the DAC.

Figure 22. 8085A Interface

Table IV. Subroutine Listing for Figure 22

2000 LOAD DAC: LXI

H,#3000

The H,L register pair

are loaded with latch

address 3000.

MVI

A,#“MS”

Load the 4 MSBs of

data into accumulator.

MOV

M,A

Transfer data from

accumulator to latch.

INR

L

Increment H,L pair to

AD7845 address.

MVI

A,#“LS”

Load the 8 LSBs of

data into accumulator.

MOV

M,A

Transfer data from

accumulator to DAC.

RET

End of routine.

MICROPROCESSOR INTERFACING

16-BIT MICROPROCESSOR SYSTEMS

Figures 19, 20 and 21 show how the AD7845 interfaces to

three popular 16-bit microprocessor systems. These are the

MC68000, 8086 and the TM32010. The AD7845 is treated as

a memory-mapped peripheral to the processors. In each case, a

write instruction loads the AD7845 with the appropriate data.

The particular instructions used are as follows:

MC68000:

MOVE

8086:

MOV

TMS32010: OUT

Figure 19. AD7845 to MC68000 Interface

Figure 20. AD7845 to 8086 Interface

Figure 21. TMS32010