MCP4021 datasheet(29/64 Pages) MICROCHIP

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DS21945E-page 29

MCP4021/2/3/4

5.0

SERIAL INTERFACE

5.1

Overview

The MCP4021/2/3/4 utilizes a simple 2-wire interface to

increment or decrement the digital potentiometer’s

wiper terminal (W), store the wiper setting in non-vola-

tile memory and turn the WiperLock technology feature

on or off. This interface uses the Chip Select (CS) pin,

while the U/D pin is the Up/Down input.

The Increment/Decrement protocol enables the device

to move one step at a time through the range of

possible resistance values. The wiper value is

initialized with the value stored in the internal EEPROM

upon power-up. A wiper value of 00h connects the

wiper to terminal B. A wiper value of 3Fh connects the

wiper to terminal A. Increment commands move the

wiper toward terminal A, but will not increment to a

value greater than 3Fh. Decrement commands move

the wiper toward terminal B, but will not decrement

below 00h.

Refer to Section 1.0 “Electrical Characteristics”,

AC/DC Electrical Characteristics table for detailed input

threshold and timing specifications.

Communication is unidirectional. Therefore, the value

of the current wiper setting cannot be read out of the

MCP402X device.

5.2

Serial Commands

The MCP402X devices support 10 serial commands.

The commands can be grouped into the following

types:

• Serial Commands

• High-voltage Serial Commands

All the commands are shown in Table 5-1.

The command type is determined by the voltage level

on the CS pin. The initial state that the CS pin must be

driven is VIH. From VIH, the two levels that the CS pin

can be driven are:

•VIL

•VIHH

If the CS pin is driven from VIH to VIL, a serial

command is selected. If the CS pin is driven from VIH to

VIHH, a high-voltage serial command is selected.

High-voltage serial commands control the state of the

WiperLock technology. This is a unique feature, where

the user can determine whether or not to “lock” or

“unlock” the wiper state.

High-voltage serial commands increment/decrement

the wiper regardless of the status of the WiperLock

technology.

TABLE 5-1:

COMMANDS

Command Name

Saves

Wiper

Value in

EEPROM

High

Voltage

on CS

pin?

After

Command

Wiper is

“locked”/

”unlocked”

Works

when

Wiper is

“locked”?

Increment without Writing Wiper Setting to EEPROM

——

unlocked

Note 1

Increment with Writing Wiper Setting to EEPROM

Yes

—

unlocked

Note 1

Decrement without Writing Wiper Setting to EEPROM

——

unlocked

Note 1

Decrement with Writing Wiper Setting to EEPROM

Yes

—

unlocked

Note 1

Write Wiper Setting to EEPROM

Yes

—

unlocked

Note 1

High-Voltage Increment and Disable WiperLock Technology

Yes

unlocked

Yes

High-Voltage Increment and Enable WiperLock Technology

Yes

locked

Yes

High-Voltage Decrement and Disable WiperLock Technology

Yes

unlocked

Yes

High-Voltage Decrement and Enable WiperLock Technology

Yes

locked

Yes

Write Wiper Setting to EEPROM and Disable WiperLock

Technology

Yes

unlocked

Yes

Write Wiper Setting to EEPROM and Enable WiperLock

Technology

Yes

locked

Yes

Note 1: This command will only complete if wiper is “unlocked” (WiperLock Technology is Disabled).

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