DS1869

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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:

≈1 second + 63 X 100 ms = 7.3 (seconds)

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

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

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.