CAT521

7

Doc. No. 2003, Rev. F

Figure 3. Temporary Change in Output

the same as that which had been there previously no

change in the DPP’s output is noticed. Had the value

held in the control register been different from that stored

in non-volatile memory then a change would occur at the

read cycle’s conclusion.

TEMPORARILY CHANGE OUTPUT

The CAT521 allows temporary changes in the DPP’s

output to be made without disturbing the settings retained

in non-volatile memory.

This feature is particularly

useful when testing for a new output setting and allows

for user adjustment of preset or default values without

losing the original factory settings.

Figure 3 shows the control and data signals needed to

effect a temporary output change. DPP settings may be

changed as many times as required. The temporary

setting remains in effect long as CS remains high. When

CS returns low the DPP will return to the output value

stored in non-volatile memory.

When it is desired to save a new setting acquired using

this feature, the new value must be reloaded into the

DPP wiper control register prior to programming. This is

because the CAT521’s internal control circuitry discards

from the programming register the new data two clock

cycles after receiving it if no PROG signal is received.

Amplified DPP Output

APPLICATION CIRCUITS

Bipolar DPP Output

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

D0

D1

D2

D3

D4

D5

D6

D7

1

NEW DPP DATA

CURRENT DPP DATA

DO

DI

CS

PROG

DPP

OUTPUT

t

1

2

3

4

5

6

7

8

9

10

11

12

N

N+1 N+2

o

CURRENT

DPP VALUE

NON-VOLATILE

NEW

DPP VALUE

VOLATILE

CURRENT

DPP VALUE

NON-VOLATILE

RDY/BSY

MSB

LSB

1111

1111

—— (.98 VREF) + .01 VREF= .990 V

V

= +4.90V

1000

0000

—— (.98 VREF) + .01 VREF= .502 V

V

= +0.02V

0111

1111

—— (.98 VREF) + .01 VREF= .498 V

V

= -0.02V

0000

0001

—— (.98 VREF + .01 VREF = .014 V

V

= -4.86V

0000

0000

—— (.98 VREF) + .01 VREF = .010 V

V

= -4.90V

REF

IF

V

= 5V

REF

255

255

OUT

DPP INPUT

DPP OUTPUT

ANALOG

R = R

OUTPUT

REF

OUT

128

255

127

255

REF

OUT

1

255

REF

OUT

REF

OUT

0

255

VFS

= 0.99 V

V

= 0.01 V

ZERO

V

= ——— (V

- V

) + V

DPP

CODE

255

FS

ZERO

ZERO

GND

VDD

CONTROL

& DATA

+

–

OP 07

-15V

+15V

+5V

RR

i

F

For R =

I

RF

V

= 2V

-V

OUT

I

DPP

Vi

VOUT

VOUT =

VDPP (RI+RF)-VIRF

RI

VREFH

VREFL

CAT521

CAT521

GND

VDD

VREFH

VREFL

CONTROL

& DATA

+

–

OP 07

VOUT

-15V

+15V

+5V

RR

I

F

V

= (1 + –––) V

OUT

DPP

RF

RI