Rainbow Electronics DS1800 User Manual

DS1800

PRODUCT PREVIEW

DS1800

Dual Inverting Log Gain/Attenuator

FEATURES

• Ultra–low power consumption

• Operates from 3V or 5V supplies

• Two digitally controlled, 128–position potentiometers

including mute

• Logarithmic Gain Characteristics

• Zero–crossing detection circuitry eliminates noise

caused by discrete wiper position changes

• Two Control Interfaces

– 3–wire serial CPU control
– Push–button control

• 20–pin DIP (300 Mil), 20–pin SOIC (300 Mil), and

20–pin (173 Mil) TSSOP packaging available

• Operating Temperature:

– Commercial: 0°C to 70°C
– Industrial: –40°C to 85°C

• Software and hardware mute

• Resistance Available: 53KΩ

PIN ASSIGNMENT

GND

1

C

2

OUT

3

CLK

4

D

5

RST

ZCEN

MODE

OUT0

6
7
8

W0

9
10

IN0

20–PIN DIP (300 MIL)

20–PIN SOIC (300 MIL)

20–PIN TSSOP

20

V

CC

19

P1G

18

P1A

17

P0G

16

P0A

15

MUTE

14

AGND

13

IN1

12

OUT1

11

W1

PIN DESCRIPTION

OUT0,OUT1 – Low–end of resistor
IN0, IN1 – High–end of resistor
W0,W1 – Wiper Terminal
V

CC

RST – Serial Port Reset Input
CLK – Serial Port Clock Input
D – Serial Port Data Input
C

OUT

P0G,P1G – Gain Input Pot Controls
P0A,P1A – Attenuation Input Pot Controls
ZCEN – Zero–Crossing Detect Input
MUTE – Hardware Mute Control Input
AGND – Analog Ground
GND – Ground

– 3V or 5V Power Supply Input

– Cascade Data Output

DESCRIPTION

The DS1800 is a dual audio–taper potentiometer
designed specifically for use in the feedback path of the
inverting configuration of an operational amplifier (see
Figure 2). In this configuration, the DS1800 provides a

relationship of –20log(RF/RI) giving a gain/attenu-

V

O/VI

ation range covering +20 dB to –63 dB. Each poten­tiometer has a total of 129 positions including mute. The
DS1800 provides five areas of resolution which include

0.25 dB per step from +20 dB to +3 dB, 0.5 dB per step
from +3 dB to –12 dB, 1 dB from –12 dB to –27 dB, and

Copyright 1995 by Dallas Semiconductor Corporation.
All Rights Reserved. For important information regarding
patents and other intellectual property rights, please refer to
Dallas Semiconductor data books.

from –27 dB to –47 dB; 2 dB per step, and from –47 dB to
–63 dB; 4 dB per step. The mute position provides 100
dB of attenuation.

The DS1800 has two control interfaces (see Figure 1).
The first is a 3–wire serial CPU interface consisting of
RST

, CLK, and D. The second interface is a contact–
closure interface, allowing easy push–button control
without the need for external debounce or timing cir­cuitry. The device also provides for software muting (via

072095 1/13

DS1800

CPU) or hardware muting (MUTE control input). The
hardware mute is a toggle type which returns the wiper
positions to their prior states. Additional information on
CPU and push–button control is described under the
section entitled “OPERATION”.

The DS1800 is available in 20–pin DIPs, SOICs, and
TSSOPs. One standard resistance grade of 53KΩ is
available for the device.

OPERATION

The DS1800 provides two 129–position 45KΩ poten­tiometers. These potentiometers are specifically
designed to operate in the configuration shown in Figure

2. Under this configuration the V0/VI relationship pro­vides the gain/attenuation function of –20log(R

F/RI

over a range of +20 dB to –63 dB. This function is illus­trated in Figure 3 as a graph of gain/attenuation versus
position. Figure 4 provides the relationship between R
and RI as a function of position.

The DS1800 has a total of 129 positions including a
mute position. Five areas of resolution are provided
over the gain/attenuation range and are illustrated in
Figure 3. From position 0 to position 68, a resolution of

0.25 dB per step is attained covering a gain/attenuation
range of +20 dB to +3 dB. From position 68 to position
98, 0.5 dB per step of resolution is attained covering +3
dB to –12 dB of gain/attenuation. Positions 98 to 113
have 1 dB per step resolution and cover a gain/attenua­tion range of –12 to –27 dB. Positions 113 to 123 pro­vide 2 dB per step and cover a gain/attenuation range of
–27 dB to –47 dB. Positions 123 to 127 provide 4 dB per
step and cover a gain/attenuation range of –47 dB to 63
dB. Position 128 is the mute position and typically pro­vides 100 dB of attenuation.

PIN DESCRIPTIONS

The DS1800 has a total of 20 pins which provide various
functions for the device. This section provides a
description of each pin’s operation.

V

– Power Supply Voltage Input. The DS1800 will

CC

support 3V or 5V power supply operation.

GND – Ground. The DS1800 has two ground pins. The
GND supports the digital ground for the device.

AGND – Analog Ground. The DS1800 has two ground
pins. The AGND supports analog ground for the device.

IN0, IN1 – Input terminals for the two respective poten­tiometers as shown in Figure 2. These terminals should
be connected to the analog signal,VI, to provide the
gain/attenuation characteristics stated. These termi­nals are referenced as INx in the Figure 2 drawing.

OUT0, OUT1 – Analog Outputs. These pins should be
connected to the output terminal of the operational
amplifier as shown in Figure 2. These inputs are refer­enced as OUTx in the Figure 2 drawing.

W0, W1 – Wiper T erminals. The wiper terminals of each
pot are connected to the inverting terminal of the opera­tional amplifier. The position of the wiper terminal is
selected either through CPU control or push–button
control.

)

P0A, P1A – Attenuation Push–button Inputs. These
push–button inputs are used to control wiper position of

F

the part . Activity on these inputs will cause the position
of the wiper to move towards the OUT0, and OUT1 ter­minals, respectively .

P0G, P1G – Gain Push–button Inputs. These push–
button inputs control wiper position and are used to
move the position of the wiper towards the IN0 and IN1
terminals, respectively .

RST

– Serial Port Reset. The RST input deactivates the
3–wire serial interface. This input is active when in the
low–state. All 3–wire communications must take place
when this input is in a high state.

CLK – Serial Clock Input. The CLK input is the positive–
edge clock signal input used for 3–wire timing synchro­nization.

D – Serial Data Input. The D input is used to input serial
data for wiper position changes.

C

– Serial Cascade Output. The C

OUT

OUT

signal used to read the contents of the current settings
of the wiper positions. As data is clocked into the D
input, data corresponding to the wipers are shifted out of

OUT

pin.

the C

MODE – Push–button Debounce Control. The MODE
pin is used to choose between a fast and slow mode of
push–button debouncing. When in a high state, push–
button debounce is slow. When in a low–state, push–

is an output

072095 2/13

DS1800

button debounce is faster. These timing differences are
discussed in the section entitled “Push–button Inter­face Control”. The state of this pin is determined only at
device power–up.

POWER–UP CONDITIONS

The position of the wipers of the DS1800 on power up
are internally set to position 127, which is the last posi­tion before mute. The user then has the responsibility of
changing the wiper position to the desired attenuation/
gain levels.

Additionally , the serial port is stable and active within 10
microseconds. The contact closure control interface
inputs are active after 50 ms.

INTERFACE CONTROL OPTIONS

Control of the DS1800 is provided via two types of inter­face ports. A 3–wire CPU control interface allows the
exact wiper positions of the potentiometers to be written
using two 8–bit words. A cascade output, C

OUT

, is pro­vided when controlling multiple devices via one CPU or
when reading the wiper positions of each potentiometer .

The second interface is a contact closure interface that
allows push–buttons to control movement of the wiper
positions. Under push–button control no external
debounce or timing circuitry is needed. A block diagram
of the DS1800 is shown in Figure 1.

3–WIRE SERIAL INTERFACE CONTROL

CPU control of the DS1800 is accomplished using the
3–Wire serial port of the device. This interface drives an
internal control logic unit. Direct wiper positioning is
accomplished by using this port which consist of three
input signals: RST, CLK, and D.

The RST
port write operations. The CLK terminal is an input that
provides synchronization for data I/O. Data is input bit
by bit via the D input signal pin.

The 3–Wire serial timing diagrams are provided in Fig­ure 5. Serial port operation or activity begins with the
transition of the RST
state. Once activated, data is clocked into the part on
the low to high transition of the CLK signal input. Data
input via the D terminal is transferred in order of the

control signal is used to enable 3–wire serial

signal from a low–state to a high–

desired potentiometer–0 wiper value, followed by the
potentiometer–1 wiper position value.

Two 8–bit values are used to store wiper position for
each potentiometer during powered conditions. These
8–bit values are written to a 16–bit I/O shift register. A
detailed diagram of the 16–bit I/O shift register is shown
in Figure 6.

Bits 0 through 7 are reserved for the positioning of
wiper–0 while bits 8 through 15 are reserved for control
of wiper–1. Bits 0 through 6 are used for actual wiper
positioning of potentiometer–0. Bit 7 is used to mute
potentiometer–0. If this bit is set to a “1”, the potentiom­eter–0 wiper will be connected to the OUT0 end of the
resistor array regardless of the settings of bits 0 through

6.

Bits 8 through 15 are used for positioning the wiper of
potentiometer–1. Bits 8 through 14 control wiper posi­tion on the resistor array. Bit 15 is used for muting poten­tiometer–1. Bit 15, like bit 7, when set to “1” will mute
potentiometer 1, regardless of the settings of bits 8
through 14.

Data is transmitted LSB first starting with bit–0. A com­plete transmission of 16 bits of data is required to insure
proper setting of each potentiometer’s wiper. An incom­plete transmission may result in undesired wiper set­tings.

Once the 16 bits of information has been transmitted
and the RST

signal input transitions to a low–state, the

new wiper positions are loaded into the part.

PUSH–BUTTON INTERFACE CONTROL

The DS1800 can be configured to operate from contact
closure or push–button inputs. The push–button inputs
consist of signals P0A, P0G, P1A, P1G and MUTE.
P0A and P0G allow attenuation and gain control of the
input signal to potentiometer–0, while P1A and P1G
provide the same control for potentiometer–1. The
MUTE input provides a toggle control for muting the
potentiometers via pushbutton.

The P0A and P1A control inputs, based on the recom­mended circuit configuration, are used to attenuate the
incoming signal by moving the wiper position towards
the OUTx terminals. The P0G and P1G control inputs

072095 3/13

DS1800

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 50KΩ 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 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
push–button 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–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 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.

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 push­button controls. When this input is driven low, the wiper
outputs of both potentiometers will be internally con­nected to the OUTx terminal of their respective poten­tiometers. 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.

072095 4/13