CAT5251

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4

SERIAL BUS PROTOCOL

The CAT5251 supports the SPI bus data transmission

protocol. The synchronous Serial Peripheral Interface (SPI)

helps the CAT5251 to interface directly with many of

today’s popular microcontrollers. The CAT5251 contains an

8-bit instruction register. The instruction set and the

operation codes are detailed in Table 13, Instruction Set on

page 9.

After the device is selected with CS going low the first

byte will be received. The part is accessed via the SI pin, with

data being clocked in on the rising edge of SCK. The first

byte contains one of the six op-codes that define the

operation to be performed.

DEVICE OPERATION

The CAT5251 is four resistor arrays integrated with an

SPI serial interface logic, four 8-bit wiper control registers

and sixteen 8-bit, non-volatile memory data registers. Each

resistor array contains 255 separate resistive elements

connected in series. The physical ends of each array are

equivalent to the fixed terminals of a mechanical

may be interchanged. The tap positions between and at the

ends of the series resistors are connected to the output wiper

point for each potentiometer is connected to its wiper

terminal at a time and is determined by the value of the wiper

control register. Data can be read or written to the wiper

control registers or the non-volatile memory data registers

via the SPI bus. Additional instructions allow data to be

transferred between the wiper control registers and each

respective potentiometer’s non-volatile data registers. Also,

the device can be instructed to operate in an “increment/

decrement” mode.

Table 2. ABSOLUTE MAXIMUM RATINGS

Parameter

Ratings

Units

Temperature Under Bias

−55 to +125

C

Storage Temperature

−65 to +150

C

V

−2.0 to +7.0

V

1.0

W

Lead Soldering Temperature (10 s)

300

C

Wiper Current

6

mA

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the

Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect

device reliability.

1. The minimum DC input voltage is –0.5 V. During transitions, inputs may undershoot to –2.0 V for periods of less than 20 ns. Maximum DC

Table 3. RECOMMENDED OPERATING CONDITIONS

Parameter

Ratings

Units

+2.5 V to +6

V

Operating Ambient Temperature (Industrial)

−40 to +85

C