MCP4021 datasheet(33/64 Pages) MICROCHIP

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DS21945E-page 33

MCP4021/2/3/4

5.2.4

DECREMENT WITH WRITING

WIPER SETTING TO EEPROM

This mode is achieved by initializing the U/D pin to a

low state (VIL) prior to achieving a low state (VIL) on the

CS pin. Subsequent rising edges of the U/D pin

decrement the wiper setting (toward terminal B). This is

shown in Figure 5-4.

After the wiper is decremented to the desired position,

the U/D pin should remain high (VIH). Then when the

CS pin is raised to VIH, the wiper value is written to the

EEPROM. Therefore, if the device voltage is lowered

below the RAM retention voltage of the device, once

the device returns to the operating range, the wiper will

be loaded with this wiper setting (stored in the

EEPROM).

To ensure that “unexpected” transitions on the U/D pin

do not cause the wiper setting to decrement, the U/D

pin should be driven low (VIL) and the CS pin forced to

VIH as soon as possible (within device specifications)

after the last desired increment occurs.

After the CS pin is driven to VIH (from VIL), all other

serial commands are ignored until the EEPROM write

cycle (tWC) completes.

FIGURE 5-4:

Decrement with Writing Wiper Setting to EEPROM.

Note:

The wiper value will not underflow. That is,

once the wiper value equals 0x00,

subsequent decrement commands are

ignored.

EEPROM

U/D

Wiper

WiperLock™ Technology

WiperLock Technology Enable

WiperLock Technology Disable

X-1

X-2

X-3

X-4

Note: If WiperLock technology enabled, wiper will not change.

VIH

VIL

tWC

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