®

DAC811

8

FIGURE 10. Right-Justified Data Bus Interface.

FIGURE 11. Left-Justified Data Bus Interface.

FIGURE 8. Addressing and Control for 4-Bit Microcom-

puter Interface.

FIGURE 9. 12-Bit Data Format for 8-Bit Systems.

D0

D4

D8

D1

D5

D9

D2

D6

D10

D3

D7

D11

16

14

10

17

13

9

18

12

8

19

11

7

DB0

DB1

DB2

DB3

WR

A

A

1

0

Base

Address

Decoder

A

A

N

2

2

3

4

5

6

WR

LDAC

N

N

N

1/2

74LS139

A

B

C

7

6

5

4

1

3

2

CS

(Chip

Select)

A

A

1

0

EN

Y

Y

Y

Y

3

2

1

0

X

X

X

X D11 D10 D9 D8

D7 D6 D5 D4 D3 D2 D1 D0

a. Right-Justified

D11 D10 D9 D8 D7 D6 D5 D4

D3 D2 D1 D0

b. Left-Justified

XXXX

D0

D8

D1

D9

D2

D10

D3

D11

D4

D5

D6

D7

16

10

17

9

18

8

19

7

14

13

12

11

DB0

DB1

DB2

DB3

DB4

DB5

DB6

DB7

WR

A

A

1

0

Base

Address

Decoder

A

A

15

2

2

3

4

5

6

WR

LDAC

N

N

N

A

B

C

CS

D4

D5

D6

D7

D8

D0

D9

D1

D10

D2

D11

D3

14

13

12

11

10

16

9

17

8

18

7

19

DB0

DB1

DB2

DB3

DB4

DB5

DB6

DB7

WR

A

A

1

0

Base

Address

Decoder

A

A

15

2

2

3

4

5

6

WR

LDAC

N

N

N

A

B

C

CS

8-BIT INTERFACE

The control logic of DAC811 permits interfacing to right-

justified data formats, as illustrated in Figure 9. When a

12-bit D/A converter is loaded from an 8-bit bus, two bytes

of data are required. Figures 10 and 11 show an addressing

scheme for right-justified and left-justified data respectively.

The base address is decoded from the high-order address

bits. A0 and A1 address the appropriate latches. Note that

adjacent addresses are used. For the right-justified case,

X1016 loads the 8LSBs, and X0116 loads the 4MSBs and

simultaneously transfers input latch data to the D/A latch.

Addresses X0016 and X1116 are not used.

Left-justified data is handled in a similar manner, shown in

Figure 11. The DAC811 still occupies two adjacent loca-

tions in the microcomputer's memory map.