CAT5127, CAT5129

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3

DEVICE OPERATION

The CAT5127 operates like a digitally controlled variable

terminals. There are 32 available tap positions including the

terminals.

The CAT5129 operates like a digitally controlled variable

and GND. There are 31 resistor elements connected in series

Operation is controlled by three inputs, INC, U/D and CS.

These inputs control a five-bit up/down counter whose

output is decoded to select the wiper position. The selected

wiper position can be stored in nonvolatile memory using

the INC and CS inputs.

With CS set LOW, the device is selected and will respond

to the U/D and INC inputs. HIGH to LOW transitions on

INC will increment or decrement the wiper (depending on

the state of the U/D input and five-bit counter). The wiper,

when at either end terminal, acts like its mechanical

equivalent and does not move beyond the last position. The

value of the counter is stored in nonvolatile memory

whenever CS transitions HIGH while the INC input is also

HIGH. When the device is powered-down, the last stored

wiper counter position is maintained in the nonvolatile

memory. When power is restored, the contents of the memory

are recalled and the counter is set to the value stored.

With INC set low, the device may be de-selected and

powered down without storing the current wiper position in

nonvolatile memory. This allows the system to always

power up to a preset value stored in nonvolatile memory.

Table 2. OPERATION MODES

INC

CS

U/D

Operation

High to Low

Low

High

Wiper toward H

High to Low

Low

Low

Wiper toward L/GND

High

Low to High

X

Store Wiper Position

Low

Low to High

X

No Store, Return to Standby

X

High

X

Standby

Figure 2. Variable Resistor Equivalent Circuit