Datasheet

MCP4021/2/3/4
DS21945E-page 30 © 2006 Microchip Technology Inc.
5.2.1 INCREMENT WITHOUT 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 5-1.
After the wiper is incremented to the desired position,
the CS
pin should be forced to V
IH
to ensure that
“unexpected” transitions (on the U/D
pin do not cause
the wiper setting to increment. 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. This is
since an EEPROM write cycle (t
wc
) is not active.
FIGURE 5-1: Increment without 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
X
XXXX
Note: If WiperLock technology enabled, wiper will not move.
V
IH
V
IH
5
6
V
IL
V
IL