DS1800 Datasheet, PDF (5/14 Pages) Dallas Semiconductor – Dual Inverting Log Gain/Attenuator

DS1800
Contact closure is defined as the transition from a high level to a low level on these input terminals. The
DS1800 interprets input pulse widths as the means of controlling wiper movement. A single pulse input
over the PxA or PxG input terminals will cause the wiper to move one position. A transition from high to
low on these inputs is considered the beginning of pulse activity or contact closure. The DS1800 has two
timing modes for controlling the speed at which pushbuttons will operate. These modes are termed fast
mode operation and slow mode operation.
In slow mode operation, a single pulse is defined as being greater than 1 ms but lasting no longer than 0.8
seconds. Correspondingly, in fast mode operation, a single pulse is defined as being greater than 50 µs
but lasting no longer than 0.8 second.
Repetitive pulsed inputs can be used to step through each resistive position of the device in a relatively
fast manner. The timing requirements for repetitive pulsed inputs is that pulses must be separated by a
minimum time of 1 ms for slow mode operation and 50 µs for fast mode operation.
Pulse inputs lasting longer than 0.8 seconds will cause the wiper to move one position every 25 ms
seconds after the initial 0.8 second hold time. This is true regardless of the mode input. The total time
required to transcend the entire potentiometer using a continuous input pulse is given by the following
formula:
0.8(seconds) + 127 x 25 ms = 3.975(seconds)
SLOW MODE AND FAST MODE OPERATION
Pushbutton operation, as mentioned, can be operated at two distinct speeds or modes; fast and slow. The
mode or speed of pushbutton debounce is determined at device power-up by the state of the MODE pin.
When MODE powers to a high state, pushbutton debounce timing will operate at the slow mode rate.
When powered and in the low state, debounce timing operates at the fast rate. Timing specifications for
pushbutton operation can be found in the AC Electrical Specification Table for pushbutton operation.
Timing diagrams for pushbutton operation can be found in Figure 7.
ZERO CROSSING DETECTION
The DS1800 provides a zero-crossing detection capability when using the 3-Wire serial interface. Zero-
crossing detection provides a means for minimizing unwanted audible noise that may result from sizable
discrete wiper transitions when using the part in audio applications. The zero-crossing detect feature
allows independent wiper changes only when the two terminals of the potentiometer(s) have equal
potentials and within a 50 ms time window from the fall of the RST signal. If at 50 ms the DS1800 has
not detected a zero-crossing, the wiper position of the potentiometer(s) will change regardless of the state
of the input signal. Zero-crossing detection is activated when the ZCEN input is in a low-state. When high,
the ZCEN input deactivates both the 50 ms time requirement and zero-crossing detection.
Zero-crossing detection is also available when using the part in pushbutton operation. When a pushbutton
is activated, the part will change wiper position during the first detected zero-crossing or at the end of a
50 ms time window.
When operating in pushbutton operation with a continuous input pulse, the wiper position will change
once during the initial 0.8-second time period. This change is dictated by a detected zero-crossing or 50
ms time window. Subsequent changes when operating with a continuous input pulse occur on 25 ms time
intervals and are dependent on zero-crossings or 50 ms time-outs.
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