Datasheet

MCP4021/2/3/4
DS21945E-page 32 © 2006 Microchip Technology Inc.
5.2.3 DECREMENT WITHOUT 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 will
decrement the wiper setting toward terminal B. This is
shown in Figure 5-3.
After the wiper is decremented to the desired position,
the U/D
pin should be forced low (V
IL
) and the CS pin
should be forced to V
IH
. This will ensure that
“unexpected” transitions on the U/D pin do not cause
the wiper setting to decrement. Driving the CS pin to
V
IH
should occur as soon as possible (within device
specifications) after the last desired increment occurs.
The EEPROM value has not been updated to this new
wiper value, so, 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 the wiper setting in the EEPROM.
After the CS
pin is driven to V
IH
(from V
IL
), any other
serial command may immediately be entered, since an
EEPROM write cycle (t
WC
) is not started.
FIGURE 5-3: Decrement without 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
1 2 3 4
WiperLock™ Technology
WiperLock Technology Enable
WiperLock Technology Disable
X-1X X-2 X-3 X-4
X
XXXX
Note: If WiperLock technology enabled, wiper will not change.
V
IH
V
IH
5
6
V
IL
V
IL
V
IL