Datasheet

MCP4021/2/3/4
DS21945E-page 34 © 2006 Microchip Technology Inc.
5.2.5 WRITE WIPER SETTING TO
EEPROM
To write the current wiper setting to EEPROM, force
both the CS
pin and U/D pin to V
IH
. Then force the CS
pin to V
IL
. Before there is a rising edge on the U/D pin,
force the CS pin to V
IH
. This causes the wiper setting
value to be written to EEPROM.
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, force the
CS
pin to V
IH
as soon as possible (within device
specifications) after the U/D
pin is forced to V
IL
.
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 5-5: Write Wiper Setting to EEPROM.
Note: After the U/D pin is forced to V
IL
, each
rising edge on the U/D
pin will cause the
wiper to increment.
This is the same command as the “Incre-
ment with Writing Wiper Setting to
EEPROM“ command, but the U/D
pin is
held at V
IL,
so the wiper is not incre-
mented.
EEPROM
U/D
CS
Wiper
WiperLock™ Technology
WiperLock Technology Enable
WiperLock Technology Disable
X+4
X
X+4
V
IH
V
IH
V
IH
5
6
V
IL
V
IL
t
WC