DS1869 Dallas Semiconducotr, DS1869 Datasheet - Page 2

• Manufacturer Part Number: DS1869
• Description: 3V Dallastat Electronic Digital Rheostat
• Manufacturer: Dallas Semiconducotr

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OPERATION
The DS1869 can be configured to operate from a single contact closure, dual contact closure, or a digital
source input. Figures 1 and 2 illustrate both contact closure configurations. Contact closure is defined as a
transition from a high level to a low level on the up contact (UC) or down contact (DC) inputs. All three
control inputs are active when in a low state and are inactive when in a high state.
The DS1869 interprets input pulse widths as the means of controlling wiper movement. A single pulse
input on the UC, DC, or D input terminals will cause the wiper position to move 1/64
resistance. A transition from a high to low on these inputs is considered the beginning of pulse activity or
contact closure. A single pulse must be greater than 1 ms but lasting no longer than 1 second. Pulse
timings are shown in Figure 5.
Repetitive pulsed inputs can be used to step through each resistive position of the device in a relatively
fast manner (see Figure 5b). The requirement for repetitive pulsed inputs is that pulses must be separated
by a minimum time of 1 ms. If the input is not allowed to be inactive (high) for at least 1 ms, the DS1869
will interpret repetitive pulses as a single 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 by the formula below:
Single contact closure operation allows the user to control wiper movement in either direction from a
single pushbutton input. Figure 1 presents a typical single pushbutton configuration. The UC input is used
to increment and decrement wiper position for single pushbutton mode of operation. The DC input
provides no functionality in this mode but must be connected to the positive supply voltage (V
digital source input (D) can be allowed to float.
On device power-up, the configuration shown in Figure 1 must exist in order to enter the single contact
closure mode of operation especially and specifically, the (DC) input’s direct connection to the positive
supply voltage (V
The initial direction of wiper movement in single pushbutton operation is determined by prior activity.
The initial direction of wiper movement will be opposite to that of the previous activity. Changing the
direction of wiper movement in single pushbutton mode is accomplished by allowing a period of
inactivity on the UC input of (greater than) 1 second, or by moving the wiper to the end of the
potentiometer range. This will occur regardless of whether the input is a continuous pulse, a sequence of
repetitive pulses or a single pulse.
The digital source input, D, was designed for microprocessor or controlled applications. This control
input manipulates the device in the same manner as the single pushbutton configuration, controlling
movement of the wiper position in both upward and downward directions. One added feature over the
single pushbutton configuration is the ability to increment or decrement wiper position at a faster rate.
Digital source input control is available regardless of the type of pushbutton configuration.
Dual pushbutton mode of operation is entered when the DC input is floated on power-up. If interfacing
contact closure control inputs to digital logic, the DC input must be interfaced to an open drain drive
which is high impedance during power-up; see Figure 2B. This will prevent the device from entering a
single pushbutton mode of operation.
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