Rainbow Electronics DS1800 - Manual (Page 4)

DS1800
072095 4/13
provide the opposite function; positioning the wiper(s)
closer to the INx terminals, thus providing gain.
Each of these control inputs are internally pulled–up via
a 50K
Ω resistance. Additionally, these inputs require no
external components for debouncing or timing which
are provided internal to the part.
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 activ-
ity or contact closure. The DS1800 has two timing
modes for controlling the speed at which pushbuttons
will operate. These modes are termed fast mode opera-
tion 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
µ s 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
µ s 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 regard-
less of the mode input. The total time required to tran-
scend 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 pow-
ered 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
push–button operation can be found in Figure 7.
ZERO CROSSING DETECTION
The DS1800 provides a zero–crossing detection capa-
bility when using the 3–Wire serial interface. Zero–
crossing detection provides a means for minimizing
unwanted audible noise that may result from sizable dis-
crete wiper transitions when using the part in audio
applications. The zero crossing detect feature allows
independent wiper changes only when the two termi-
nals of the potentiometer(s) have equal potentials and
within a 50 ms time window from the fall of the RST sig-
nal. 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–detection
crossing.
Zero crossing detection is also available when using the
part in push–button operation. When a push–button 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 push–button operation with a contin-
uous 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 win-
dow. Subsequent changes when operating with a con-
tinuous input pulse occur on 25 ms time intervals and
are dependent on zero crossings or 50 ms time–outs.
MUTE CONTROL
The DS1800 provides a mute control feature which can
be accessed by the user through hardware or software.
Hardware control of the device is achieved through the
MUTE input pin. This pin is internally pulled up through
a 50K resistor and functions like the PxG and PxA push-
button controls. When this input is driven low, the wiper
outputs of both potentiometers will be internally con-
nected to the OUTx terminal of their respective poten-
tiometers. This input performs as a toggle input, with the
first activity on this pin connecting the wiper terminals to
the OUTx terminals (position 128) of the potentiometer.
The next input activity on this pin will return the wiper
position to the previous state before muting occurred.