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DS1668 Datasheet, PDF (4/10 Pages) Dallas Semiconductor – ELECTRONIC DIGITAL RHEOSTAT
DS1668, DS1669, DS1669S
Dallastats interpret input pulse widths as the means of
controlling wiper movement. A single pulse width input
over the UC, DC, or D terminals will cause the wiper
position to move 1/64th of the total resistance. All
inputs, UC, DC, or D, are inactive when in the high state.
A transition from a high to low on these inputs is consid-
ered the beginning of pulse activity.
A single pulse is defined as being greater than 1 ms but
lasting no longer than a second when using the contact
closure inputs UC and DC. When using the D input a
single pulse is defined as being greater than 1 µs but
lasting no longer than 1 second. This is shown in Fig-
ures 4a and 6a. Repetitive pulsed inputs can be used to
step through each resistive position of the device (see
Figures 4a and 6b). The requirement for repetitive
pulsed inputs is that pulses must be separated by a
minimum time of 1 ms. If not, the Dallastat will interpret
repetitive pulses as a single continuous pulse.
Pulse inputs lasting longer than 1 second will cause the
wiper to move one position every 100 ms following the
initial 1 second hold time. The total time to transcend the
entire potentiometer using a continuous input pulse is
given in the equation below:
1 (second) + 63 X 100 ms = 7.3 (seconds)
In single pushbutton mode or when using the digital
source input, as the wiper reaches the end of the poten-
tiometer its direction of movement reverses. This will
occur whether or not the input is a continuous pulse or a
sequence of repetitive pulses. Changing the direction of
wiper movement in single pushbutton mode or digital
source mode is also accomplished by a period of inac-
tivity on the UC or D inputs for (minimum) 1 second or
greater. In dual pushbutton mode, the direction is con-
trolled by the UC and DC inputs. No wait states are
required to change wiper direction in dual pushbutton
mode. Additionally, in dual pushbutton mode as the
wiper reaches the end of the potentiometer, the direc-
tion of wiper movement will not change. Wiper position
will remain at the potentiometers’ end until an opposite
direction input is given.
All control inputs, UC, DC, and D, are internally pulled
up with a 100K ohm resistance. Additionally, the UC and
DC inputs are internally debounced and require no
external components for input signal conditioning.
The DS1668/DS1669 are provided with two supply
inputs –V and +V. The maximum voltage difference
between the two supply inputs is + 8.0 volts while the
minimum voltage difference is +4.5 volts. All input levels
are referenced to the negative supply input, –V. The volt-
age applied to any Dallastat terminal must not exceed the
negative supply voltage (–V ) by –0.5 or the positive sup-
ply voltage (+V) by + 0.5 volts. The minimum logic high
level must be +2.4 volts with reference to the –V supply
voltage input. A logic low level with reference to the –V
supply voltage has a maximum value of +0.8 volts. Dal-
lastats exhibit a typical wiper resistance of 400 ohms with
a maximum wiper resistance of 1000 ohms. The maxi-
mum wiper current allowed through the Dallastat is speci-
fied at 1 milliamps (see DC Electrical Characteristics).
NONVOLATILE WIPER SETTINGS
Dallastats maintain the position of the wiper in the
absence of power. This feature is provided through the
use of EEPROM type memory cell arrays. During nor-
mal operation the position of the wiper is determined by
the input multiplexer. Periodically, the multiplexer will
update the EEPROM memory cells. The manner in
which an update occurs has been optimized for reliabil-
ity, durability, and performance. Additionally, the update
operation is totally transparent to the user.
When power is applied to the Dallastat, the wiper setting
will be the last recorded in the EEPROM memory cells.
If the Dallastat setting is changed after power is applied,
the new value will be stored after a delay of 2 seconds.
The initial storage of a new value after power–up,
occurs when the first change is made, regardless of
when this change is made.
After the initial change on power–up, subsequent
changes in the Dallastat EEPROM memory cells will
occur only if the wiper position of the part is moved
greater than 12.5% of the total resistance range. Any
wiper movement after initial power–up which is less
than 12.5% will not be recorded in the EEPROM
memory cells. Since the Dallastat contains a 64–to–1
multiplexer, a change of greater than 12.5% corre-
sponds to a change of the fourth LSB.
Changes or storage to the EEPROM memory cells must
allow for a 2 second delay to guarantee that updates will
occur. The EEPROM memory cells are specified to
accept greater than 80,000 writes before a wear–out
condition. If the EEPROM memory cells do reach a
wear–out condition, the Dallastat will still function prop-
erly while power is applied. However, on power–up the
device’s wiper position will be that of the position last
recorded before memory cell wear out.
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