MCP433X datasheet(44/88 Pages) MICROCHIP

44 / 88 page

MCP433X/435X

DS22242A-page 44

 2010 Microchip Technology Inc.

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 connection, 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) con-

nected 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

RWB

RABN

256



--------------RW

N = 0 to 256 (decimal)

RWB

RABN

128



--------------RW

N = 0 to 128 (decimal)

8-bit Device

7-bit Device

TABLE 5-1:

VOLATILE WIPER VALUE VS.

WIPER POSITION MAP

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

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