Datasheet

© 2006 Microchip Technology Inc. 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 (V
IL
) prior to achieving a low state (V
IL
) 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 (V
IH
). Then when the
CS
pin is raised 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 decrement, the U/D
pin should be driven low (V
IL
) 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 5-4: 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
CS
Wiper
WiperLock™ Technology
WiperLock Technology Enable
WiperLock Technology Disable
X-1
X
X-2 X-3 X-4
XXXXX
X-4
1 2 3 4
Note: If WiperLock technology enabled, wiper will not change.
V
IH
V
IH
5
6
V
IL
V
IL
t
WC