Datasheet

© 2006 Microchip Technology Inc. DS21945E-page 31
MCP4021/2/3/4
5.2.2 INCREMENT WITH WRITING WIPER
SETTING TO EEPROM
This mode is achieved by initializing the U/D pin to a
high state (V
IH
) prior to achieving a low state (V
IL
) on the
CS pin. Subsequent rising edges of the U/D pin
increment the wiper setting toward terminal A. This is
shown in Figure 5-2.
After the wiper is incremented to the desired position,
the U/D
pin should be driven low (V
IL
). Then when the
CS
pin is forced to V
IH
, 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 increment, the U/D pin
should be driven low and the CS pin forced to V
IH
as
soon as possible (within device specifications) after the
last desired increment occurs.
After the CS
pin is driven to V
IH
(from V
IL
), all other
serial commands are ignored until the EEPROM write
cycle (t
wc
) completes.
FIGURE 5-2: Increment with Writing Wiper Setting to EEPROM.
Note: The wiper value will not overflow. That is,
once the wiper value equals 0x3F,
subsequent increment commands are
ignored.
EEPROM
U/D
CS
Wiper
1 2 3 4
WiperLock™ Technology
WiperLock Technology Enable
WiperLock Technology Disable
X+1
X
X+2 X+3 X+4
XXXXX
X+4
Note: If WiperLock technology enabled, wiper will not move.
V
IH
V
IH
V
IH
5
6
V
IL
V
IL
t
WC