MCP4441 datasheet(50/100 Pages) MICROCHIP

50 / 100 page

MCP444X/446X

DS22265A-page 50

5.2

Wiper

Each tap point (between the RS resistors) is a

connection point for an analog switch. The opposite

side of the analog switch is connected to a common

signal which is connected to the Terminal W (Wiper)

pin.

A value in the volatile wiper register selects which

analog switch to close, connecting the W terminal to

the selected node of the resistor ladder.

The wiper can connect directly to Terminal B or to

Terminal A. A zero scale connections, connects the

Terminal W (wiper) to Terminal B (wiper setting of

000h). A full scale connection, connects the Terminal W

(wiper) to Terminal A (wiper setting of 100h or 80h). In

these configurations, the only resistance between the

Terminal W and the other Terminal (A or B) is that of the

analog switches.

A wiper setting value greater than full scale (wiper

setting of 100h for 8-bit device or 80h for 7-bit devices)

will also be a Full Scale setting (Terminal W (wiper)

connected to Terminal A). Table 5-1 illustrates the full

wiper setting map.

Equation 5-2 illustrates the calculation used to

determine the resistance between the wiper and

terminal B.

EQUATION 5-2:

RWB CALCULATION

TABLE 5-1:

VOLATILE WIPER VALUE VS.

WIPER POSITION MAP

5.3

WiperLock Technology

The MCP44XX device’s WiperLock technology allows

application-specific calibration settings to be secured in

the EEPROM without requiring the use of an additional

write-protect pin. There are four WiperLock Technology

configuration bits (WL0, WL1, WL2, and WL3). These

bits prevent the Nonvolatile and Volatile addresses and

bits for the specified resistor network from being writ-

ten.

The WiperLock technology prevents the serial

commands from doing the following:

• Changing a volatile wiper value

• Writing to the specified nonvolatile wiper memory

location

• Changing the related volatile TCON register bits

For either Resistor Network 0, Resistor Network 1,

Resistor Network 2, or Resistor Network 3 (Potx), the

WLx bit controls the following:

• Nonvolatile Wiper Register

• Volatile Wiper Register

• Volatile TCON register bits RxHW, RxA, RxW, and

RxB

High Voltage commands are required to enable and

disable WiperLock. Please refer to the Modify Write

Protect or WiperLock Technology (High Voltage)

command for operation.

5.3.1

POR/BOR OPERATION WHEN

WIPERLOCK TECHNOLOGY

ENABLED

The WiperLock Technology state is not affected by a

POR/BOR event. A POR/BOR event will load the

Volatile Wiper register value with the Nonvolatile Wiper

Wiper Setting

Properties

7-bit

8-bit

3FFh –

081h

3FFh –

101h

Reserved (Full Scale (W = A)),

Increment and Decrement

commands ignored

080h

100h

Full Scale (W = A),

Increment commands ignored

07Fh –

041h

0FFh –

081h

W = N

040h

080h

W = N (Mid Scale)

03Fh –

001h

07Fh –

001h

W = N

000h

Zero Scale (W = B)

Decrement command ignored

ABN

256

()

--------------R

N = 0 to 256 (decimal)

ABN

128

()

--------------R

N = 0 to 128 (decimal)

8-bit Device

7-bit Device

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