MCP413X datasheet(38/88 Pages) MICROCHIP

38 / 88 page

MCP413X/415X/423X/425X

DS22060B-page 38

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 connections, 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 deter-

mine the resistance between the wiper and terminal B.

EQUATION 5-2:

RWB CALCULATION

TABLE 5-1:

VOLATILE WIPER VALUE VS.

WIPER POSITION MAP

A POR/BOR event will load the Volatile Wiper register

value with the default value. Table 5-2 shows the

default values offered. Custom POR/BOR options are

available. Contact the local Microchip Sales Office.

TABLE 5-2:

DEFAULT FACTORY

SETTINGS SELECTION

Wiper Setting

Properties

7-bit Pot 8-bit Pot

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

081

W = N

040h

080h

W = N (Mid-Scale)

03Fh

001h

07Fh

001

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

Wiper Code

8-bit

7-bit

-502

5.0 kΩ

Mid-scale

80h

40h

-103

10.0 kΩ

Mid-scale

80h

40h

-503

50.0 kΩ

Mid-scale

80h

40h

-104

100.0 kΩ

Mid-scale

80h

40h

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