AD8600

REV. 0

–11–

Unipolar Output Operation

The AD8600 is configured to give unipolar operation. The full-

scale output voltage is equivalent to the reference input voltage

minus 1 LSB. The output is dependent upon the digital code

and follows Table III. The actual numbers given for the analog

output are calculated assuming a +2.5 V reference.

Table III. Unipolar Code Table

DAC

Binary Input

MSB

LSB

Analog Output

1 1 1 1 1 1 1 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 0

0 1 1 1 1 1 1 1

0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0

Bipolar Output Operation

The AD8600 can be configured for bipolar operation with the

addition of an op amp for each output as shown in Figure 20.

The output will now have a swing of

±V

IV. This modification is only needed on those channels that re-

quire bipolar outputs. For channels which only require unipolar

output, no external amplifier is needed. The OP495 quad am-

plifier is chosen for the external amplifier because of its low

power, rail-to-rail output swing, and DC accuracy. Again, the

values calculated for the analog output are based upon an as-

sumed +2.5 V reference.

OUT

ø

1/4

OP495

+5V

–5V

R1

10k

V

OUT

R1

10k

V

REF

V

REF

AD8600

Figure 20. Circuit for Bipolar Output Operation

Table IV. Bipolar Code Table

DAC

Binary Input

MSB

LSB

Analog Output

1 1 1 1 1 1 1 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 0

0 1 1 1 1 1 1 1

0 0 0 0 0 0 0 1

0 0 0 0 0 0 0 0

Interfacing to the 68HC11 Microcontroller

The 68HC11 is a popular microcontroller from Motorola,

which is easily interfaced to the AD8600. The connections be-

tween the two components are shown in Figure 21. Port C of

the 68HC11 is used as a bidirectional input/output data port to

write to and read from the AD8600. Port B is used for address-

ing and control information. The bottom 4 LSBs of Port B are

the address, and the top 4 MSBs are the control lines (LD, CS,

EN

, and R/W). The microcode for the 68 HC11 is shown in

Figure 22. The comments in the program explain the function

of each step. Three routines are included in this listing: read

from the AD8600, write to the AD8600, and a continuous loop

that generates a saw-tooth waveform. This loop is used in the

application below.

DB0–DB7

A0–A3

LD

EN

R/W

CS

DGND1, DGND2

DACGND

8

4

DIGITAL GROUND

ANALOG GROUND

AD8600

MOTOROLA

68HC11

PC0–PC7

PB0–PB3

PB4

PB5

PB6

PB7

GND

Figure 21. Interfacing the 68HC11 to the AD8600