LMC1983 Digitally-Controlled Stereo Tone and Volume Circuit with Three Selectable Stereo Inputs General Description The LMC1983 is a monolithic integrated circuit that provides volume, balance, tone (bass and treble), loudness controls and selection between three pairs of stereo inputs. These functions are digitally controlled through a three-wire communication interface. There are two digital inputs for easy interface to other audio peripherals such as stereo decoders. The LMC1983 is designed for line level input signals (300 mV – 2V) and has a maximum gain of b0.5 dB. Volume is set at minimum and tone controls are flat when supply voltage is first applied. Low noise and distortion result from using analog switches and poly-silicon resistor networks in the signal path. Additional tone control can be achieved using the LMC835 stereo 7-band graphic equalizer connected to the LMC1983’s SELECT OUT/SELECT IN external processor loop. Y Y Y Y Y Y Y Y Y Y Loudness compensation 40 position 2 dB/step volume attenuator plus mute Independent left and right volume controls Low noise-suitable for use with DNRÉ and DolbyÉ noise reduction External processor loop Signal handling suitable for compact discs Pop-free switching Serially programmable: INTERMETAL bus (IM) interface 6V to 12V single supply operation 28 Pin DIP or PLCC Package Applications Y Y Y Y Y Features Y Y Stereo television Music reproduction systems Sound reinforcement systems Electronic music (MIDI) Personal computer audio control Low noise and distortion Three pairs of stereo inputs Block Diagram TL/H/11279 – 1 DNRÉ is a registered trademark of National Semiconductor Corporation. DolbyÉ is a registered trademark of Dolby Labs. C1995 National Semiconductor Corporation TL/H/11279 RRD-B30M75/Printed in U. S. A. LMC1983 Digitally-Controlled Stereo Tone and Volume Circuit with Three Selectable Stereo Inputs February 1995 Absolute Maximum Ratings (Notes 1 and 2) Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. b 65§ C to a 150§ C Lead Temperature N Package, (Soldering, 10 Seconds) V Package, (Vapor Phase, 60 Seconds) Infrared, (15 Seconds) Supply Voltage (V a b GND) 15V Voltage at any Pin GND b 0.2V to V a a 0.2V Input Current at any Pin (Note 3) 5 mA Package Input Current (Note 3) 20 mA Power Dissipation (Note 4) 500 mW a 125§ C Junction Temperature a 260§ C 215§ C 220§ C ESD Susceptability (Note 5) 2 kV Operating Ratings (Notes 1 and 2) Temperature Range TMIN s TA s TMAX b 40§ C s TA s a 85§ C LMC1983CIN, LMC1983CIV 6V to 12V Supply Voltage Range (V a b Vb) Electrical Characteristics The following specifications apply for V a e 9V, fIN e 1 kHz, input signal (300 mV) applied to INPUT 1, volume e 0 dB, bass e 0 dB, treble e 0 dB, and loudness is off unless otherwise specified. All limits apply for TA e TJ e a 25§ C. Symbol Parameter Conditions IS Supply Current VIN Input Voltage Clipping Level (1.0% THD), Select Out (Pins 7, 22) THD Total Harmonic Distortion Left and Right channels; Output Pins 13, 16 VIN e 0.3 Vrms; fIN e 100 Hz, 1 kHz, 10 kHz VIN e 2.0 Vrms; fIN e 100 Hz, 1 kHz VIN e 2.0 Vrms; fIN e 10 kHz VIN e 0.5 Vrms; Bass and Treble Tone Controls Set at Maximum VIN e 0.3 Vrms; Volume Attenuator at b20 dB, Bass and Treble Tone Controls Set at Maximum DC Shifts VIN e 0.3 Vrms; between Any Two Adjacent Control Settings VIN e 0.3 Vrms; All Mode and Input Positions Typical (Note 6) Limit (Note 7) Unit (Limit) 15 25 mA (max) 2.3 2.0 Vrms (min) 0.008 0.1 % (max) 0.4 1.0 % (max) 0.5 1.0 % (max) 0.07 0.5 % (max) 0.06 0.15 % (max) 2.0 4.0 mV (max) 18 20 mV (max) ROUT AC Output Impedance Pins 7, 22, (470X to Ground at Input) Pins 13, 16 150 26 200 40 X (max) X (max) RIN AC Input Impedance Pins 4, 5, 23, 24, 25 50 72 35 kX (max) kX (min) Volume Attenuator Range Pins 13, 16; Volume Attenuation at 0100010XXX000000 (0 dB) 0100010XXX101XXX (80 dB); (Relative to Attenuation at the 0 dB Setting) 0.5 1.5 dB (max) 80 78 82 dB (min) dB (max) 2.0 1.5 2.5 dB (min) dB (min) g 0.1 g 1.5 dB (min) g 2.0 dB (min) 86 dB (max) Volume Step Size Channel-to-Channel Tracking Error Mute Attenuation All Volume Attenuation Settings from 0100010XXX101XXX (80 dB) to 0100010XXX000000 (0 dB) (Note 9) All Volume Attenuation Settings from 0100010XXX100110 (76 dB) to 0100010XXX000000 (0 dB) from 0100010XXX101XXX (80 dB) to 0100010XXX100111 (78 dB) VIN e 1.0 Vrms 105 2 Electrical Characteristics The following specifications apply for V a e 9V, fIN e 1 kHz, input signal (300 mV) applied to INPUT 1, volume e 0 dB, bass e 0 dB, treble e 0 dB, and loudness is off unless otherwise specified. All limits apply for TA e TJ e a 25§ C. (Continued) Symbol Typical (Note 6) Limit (Note 7) Unit (Limit) fIN e 100 Hz, Pins 13, 16 g 12 g 10.0 g 14.0 dB (min) dB (max) Bass Tracking Error fIN e 100 Hz, Pins 13, 16 g 0.1 g 1.5 dB (max) Bass Step Size fIN e 100 Hz, Pins 13, 16 (Relative to Previous Level) 2.0 1.5 2.5 dB (min) dB (max) Treble Gain Range fIN e 10 kHz, Pins 13, 16 g 12 g 10.0 g 14.0 dB (min) dB (max) Treble Tracking Error fIN e 10 kHz, Pins 13, 16 g 0.1 g 1.5 dB (max) Treble Step Size fIN e 10 kHz, Pins 13, 16 (Relative to Previous Level) 2.0 1.5 2.5 dB (min) dB (max) Frequency Response VIN Applied to Input 1 and Input 2; fIN e 20 Hz b 20 kHz (Relative to Signal Amplitude at 1 kHz) g 0.1 g 1.0 dB (max) 11.5 13.5 9.5 8.5 4.5 dB (max) dB (min) dB (max) dB (min) Parameter Bass Gain Range Loudness Conditions Volume Attenuator e 40 dB, Loudness on (See Figure 5 ) Gain at 100 Hz (Referenced to Gain at 1 kHz) Gain at 10 kHz (Referenced to Gain at 1 kHz) 6.5 Signal-to-Noise Ratio VIN e 1.0 Vrms, A Weighted, Measured at 1 kHz, RS e 470X 95 90 dB (min) Channel Balance All Volume Settings 0.2 1.0 dB (max) Channel Separation Input Pins 4, 25: Output Pins 13, 16; VIN e 1.0 Vrms (Note 8) 80 60 dB (min) Input-Input Isolation 470X to AC Ground on Unused Input 95 60 dB (min) PSSR Power Supply Rejection Ratio V a e 9 VDC; 200 mVrms, 100 Hz Sinewave Applied to Pin 26 32 28 dB (min) fCLK Clock Frequency 5.0 1.0 MHz (max) VIN(1) Logic ‘‘1’’ Input Voltage Pins 1, 27, 28 (IM Bus) Pins 2, 3 1.3 2.9 2.0 5.5 V (min) V (min) VIN(0) Logic ‘‘0’’ Input Voltage Pins 1, 27, 28 (IM Bus) Pins 2, 3 0.4 1.2 0.8 3.5 V (max) V (max) VOUT(1) Logic ‘‘1’’ Output Voltage Pin 28 (IM Bus) VOUT(0) Logic ‘‘0’’ Output Voltage Pin 28 (IM Bus) 0.4 2.0 V (min) 0.8 V (max) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the deivce may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are specified with respect to ground. Note 3: When the input voltage (VIN) at any pin exceeds the power supply voltages (VIN k Vb or VIN l V a ) the absolute value of the current at that pin should be limited to 5 mA or less. The 20 mA package input current limits the number of pins that can exceed the power supply voltages with 5 mA current limit to four. Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, iJA, and the ambient temperature TA. The maximum allowable power dissipation is PD e (TJMAX b TA)/iJA or the number given in the Absolute Maximum Ratings, whichever is lower. For the LMC1983CIN, TJMAX e a 125§ C, and the typical junction-to-ambient thermal resistance, when board mounted, is 67§ C/W. Note 5: Human body model; 100 pF discharged through a 1.5 kX resistor. Note 6: Typicals are at TJ e a 25§ C and represent the most likely parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 8: The Input-Input Isolation is tested by driving one input and measuring the output when the undriven input are selected. Note 9: The Volume Step Size is defined as the change in attenuation between any two adjacent volume attenuation settings. The nominal Volume Step Size is 2 dB. 3 Typical Performance Characteristics Supply Current vs Supply Voltage Output Voltage vs Supply Voltage THD vs Load Impedance THD vs Load Impedance CCIR Output Noise vs Volume Setting Channel Separation vs Frequency THD vs VIN (VOUT Constant) THD vs Frequency Mute Gain vs Frequency Tone Control Response with Equal Bass and Treble Control Settings Loudness Response vs Frequency Select Input Impedance vs Frequency TL/H/11279 – 9 4 Connection Diagram TL/H/11279 – 2 Top View Order Number LMC1983CIN See NS Package Number N28B TL/H/11279 – 10 Top View Order Number LMC1983CIV See NS Package Number V28A Pin Description TONE IN (9, 20) CLK (1) The INTERMETAL (IM) Bus clock is applied to the CLOCK pin. This input accepts a TTL or CMOS level signal. The input is used to clock the DATA signal. A data bit must be valid on the rising clock edge. DIGITAL INPUT Internally tied high to V a through a 1 & 2 (2, 3) 30 kX pull-up resistor, these inputs allow a peripheral device to place any singlebit, active low digital information onto the IM Bus. It is then sent out to the controlling device through the DATA pin. Examples of such information could include indication of the presence of a Second Audio Program (SAP) or an FM stereo carrier. INPUTS 1, 2 & 3 These are the LMC1983’s three stereo (4, 25; 5, 24; input pairs. 6, 23) SELECT OUT The selected INPUT signal is available (7, 22) at this output. This feature allows external signal processors such as noise reduction or graphic equalizers to be used. This output can typically sink 1 mA. These pins should be capacitively coupled to pins 8 and 21, respectively, if no external processor is used. SELECT IN These are the inputs that an external sig(8, 21) nal processor uses to return a signal to the LMC1983. These pins should be capacitively coupled to pins 7 and 22, respectively, if no external processor is used. TONE OUT (10, 19) OP AMP OUT (11, 18) LOUDNESS (12, 17) MAIN OUTPUT (13, 16) BYPASS (14) GROUND (15) V a (26) ID (27) 5 These are the inputs to the tone control amplifier. See the Application Information section titled ‘‘Tone Control Response’’. Tone control amplifier output. See the Application Information section titled ‘‘Tone Control Response’’. These outputs are used with external tone control capacitors. Internally, this output is applied to the volume attenuators. The output signal on these pins is a voltage taken from the volume attenuator’s b 40 dB tap point. An external R – C network is connected to these pins. The output signal from these pins drives a stereo power amplifier. The output can typically sink 1 mA. A 10 mF capacitor is connected between this pin and ground to provide an AC ground for the internal half-supply voltage reference. This pin is connected to analog ground. This is the power supply connection. The LMC1983 is operational with supply voltages from 6V to 12V. This pin should be bypassed to ground through a 1.0 mF capacitor. This is the IDENTITY digital input that, when low, signals the LMC1983 to receive, from a controlling device, a device address (40H –47H), present on the DATA line. op amps, and poly-silicon resistors make it possible to achieve an order of magnitude quality improvement over other bipolar circuits that use analog multipliers to accomplish gain adjustment. Internal circuits set the volume to minimum, tone controls to flat, the mute to on, and all other functions off when power is first applied. Individual left and right volume controls are software programmed to achieve the stereo balance function. Figure 1 shows the connection diagram of a typical LMC1983 application. The LMC1983 has internal decoding logic that allows a microprocessor (mP) or microcontroller (mC) to communicate directly to the audio control circuitry through an INTERMETAL (IM) Bus interface. This three-wire interface consists of a bi-directional DATA line, a Clock (CLK) input line, and an Identity (ID) line. Address and function selection data (8 bits) are serially shifted from the controller to the LMC1983. This is followed by 8 bits of function value data. Data present in the internal shift register is latched and the instruction is executed. Pin Description (Continued) DATA (28) This is the serial data input for communications sent by a controller. The controller must have open drain outputs used with external pull-up resistors. The data rate has a maximum frequency of 1 MHz. The LMC1983 requires 16 bits of data to control or change a function: the first 8 bits select the LMC1983 and one of eight functions. The final eight bits set the function to a desired value. The data must be valid on the rising edge of the CLOCK input signal. General Information The LMC1983 is a CMOS/bipolar building block intended for high fidelity audio signal processing. It is designed for line level inputs signals (300 mV b 2V) and has a maximum gain of b0.5 dB. While the LMC1983 is manufactured with CMOS processing, NPN transistors are used to build low noise op amps. The combination of CMOS switches, bipolar TL/H/11279 – 3 FIGURE 1. Typical Application 6 Application Information couple the SELECT OUT signals directly to pins 8 and 21, respectively. INPUT SELECTOR The LMC1983’s input selector and mode control are shown in Figure 2 . The input selector selects one of three stereo signal sources or a mute function with typical attenuation of 100 dB. The selected signals are then sent to a mode control matrix. As shown in Table I, the matrix provides normal stereo or can direct any given channel to both LEFT or RIGHT SELECT OUTPUTs. The third matrix mode is normal stereo. The control matrix output is buffered and appears on each channel’s respective SELECT OUT pin (7, 22). Switching noise is kept to a minimum when mute is selected by using a 50 kX bias resistor. Noise performance is optimized through the use of emitter followers in the mode control matrix’s output. Internal 50 kX resistors are connected to each input selector pin to provide the proper bias point for the emitter follower buffers. Each internal 50 kX bias resistor is connected to a common halfsupply (V a /2) source. This produces a voltage at pins 7 and 22 (SELECT OUT) that is 1.4V below V a /2 (typically 3.1V with V a e 9V). Since a DC voltage is present at the input pins (4, 5, 6, 23, 24, and 25), input signals should be AC coupled through a 1 mF capacitor. The output signal at pins 7 and 22 can be used to drive exteral audio processing circuits such as noise reduction (LM1894 –DNR or Dolby) or graphic equalizers (LMC835). It is important that if any noise reduction is used it be placed ahead of any tone controls or equalizers in the external circuit path to preserve the frequency spectrum of the selected input signal. Otherwise, any frequency equalization could prevent the proper operation of the noise reduction circuit. If no external processor is used, a capacitor should be used to MINIMUM LOAD IMPEDANCE The LMC1983 employs emitter-followers to buffer the selected stereo channels. The buffered signals are available at pins 7 and 22 (SELECT OUT). The SELECT OUT buffers operate with a typical bias current of 1 mA. The Electrical Specifications table lists a maximum input signal of 2.0 Vrms (2.8 Vpeak) for 1% THD at the SELECT OUT pins. This distortion level is achieved when the minimum AC load impedance seen by the SELECT OUT pins is 2.5 kX (2.5V/1 mA). Using lower load impedances results in clipping at lower output levels. If the load impedance is DC-coupled, an increased quiescent current can flow. Latch-up may occur if the total emitter current exceeds 5 mA. Thus, maximum output voltage can be increased and much lower distortion levels can be achieved using load impedances of at least 25 kX. INPUT IMPEDANCE The input impedance of pins 4, 5, 6, 23, 24 and 25 is defined by internal bias resistors and is typically 50 kX. The SELECT IN pins have an input impedance that varies with the BASS and TREBLE control settings. The input impedance is 100 kX at DC and 19 kX at 1 kHz when the controls are set at 0 dB. Minimum input impedance of 30.4 kX at DC and 16 kX at 1 kHz occurs when maximum boost is selected. At 10 kHz the minimum input impedance, with the tone controls flat, is 6.8 kX and, with the tone controls at maximum boost, is 2.5 kX. TL/H/11279 – 4 FIGURE 2. Input and Mode Select Circuitry 7 Application Information (Continued) TABLE I. IM Bus Programming Codes for LMC1983 Address (A7 – A0) Function Data Function Selected 01000000 Input Select a Mute XXXXXX00 XXXXXX01 XXXXXX10 XXXXXX11 INPUT1 INPUT2 INPUT3 MUTE 01000001 Loudness XXXXXXX0 XXXXXXX1 Loudness OFF Loudness ON 01000010 Bass XXXX0000 XXXX0011 XXXX0110 XXXX1001 XXXX11XX b 12 dB b 6 dB XXXX0000 XXXX0011 XXXX0110 XXXX1001 XXXX11XX b 12 dB b 6 dB 01000011 01000100 01000101 Treble Left Volume Right Volume FLAT a 6 dB a 12 dB FLAT a 6 dB a 12 dB XX000000 XX010100 XX101XXX XX11XXXX b 40 dB b 80 dB b 80 dB 0 dB XX000000 XX010100 XX101XXX XX11XXXX b 40 dB b 80 dB b 80 dB 0 dB 01000110 Mode Select XXXXX100 XXXXX101 XXXXX11X Left Mono Stereo Right Mono 01000111 Read Digital Input 1 or Digital Input 2 on IM Bus XXXXXXD1D0 D0 e Digital Input 1 D1 e Digital Input 2 8 Application Information (Continued) response is achieved when C2 e C3. However, with C2 e 2(C3) and the tone controls set to ‘‘flat’’, the frequency response will be flat at 20 Hz and 20 kHz, and a 6 dB at 1 kHz. The frequency where a tone control begins to deviate from a flat response is referred to as the turn-over frequency. With C e C2 e C3, the LMC1983’s treble turn-over frequency is nominally EXTERNAL SIGNAL PROCESSING The SELECT OUT pins (7 and 22) enable greater system design flexibility by providing a means to implement an external processing loop. This loop can be used for noise reduction circuits such as DNR (LM1894) or multi-band graphic equalizers (LMC835). If both are used, it is important to ensure that the noise reduction circuitry precede the equalization circuits. Failure to do so results in improper operation of the noise reduction circuits. The system shown in Figure 3 utilizes the external loop to include DNR and a multi-band equalizer. 1 2qC(14 kX) The bass turn-over frequency is nominally 1 fBT e 2qC(30.4 kX) when maximum boost is chosen. The inflection points (the frequencies where the boost or cut is within 3 dB of the final value) are for treble and bass fTT e TONE CONTROL RESPONSE Bass and treble tone controls are included in the LMC1983. The tone controls use just two external capacitors for each stereo channel. Each has a corner frequency determined by the value of C2 and C3 (see Figure 4 ) and internal resistors in the feedback loop of the internal tone amplifier. The maximum-boost or cut is determined by the data sent to the LMC1983 (see Table I). The typical tone control response shown in Typical Performance Curves were generated with C2 e C3 e 0.0082 mF and show the response for each step. When modifying the tone control response it is important to note that the ratio of C3 and C2 sets the mid-frequency gain. Symmetrical tone 1 2qC(1.9 kX) 1 fBI e 2qC(169.6 kX) fTI e TL/H/11279 – 5 FIGURE 3. System Block Diagram Utilizing the External Processing Loop (One Channel Shown) 9 Application Information (Continued) of boost is dependent on the volume attenuator’s setting. The loudness characteristic, with the volume attenuator set at 40 dB, has a transfer function of VO (sC5R2 a 1)[sC4(R1 a 156k) a 1] e VI (s2)C4C5R2(163k) a s[C4(156k) a C5(4.9R2 a 156k)] a 1 The external components R1 and C4 can be eliminated and pin 11(18) left open if bass boost is the only desired loudness characteristic. TL/H/11279–6 FIGURE 4. The Tone Control Amplifier Increasing the values of C2 and C3 decreases the turnover and inflection frequencies: i.e., the Tone Control Response Curves shown in Typical Performance Curves will shift left when C2 and C3 are increased and shift right when C2 and C3 are decreased. With C2 e C3 e 0.0082, 2 dB steps are achieved at 100 Hz and 10 kHz. Changing C2 and C3 to 0.01 mF shifts the 2 dB per step frequency to 72 Hz and 8.3 kHz. If the tone control capacitors’ size is decreased these frequencies will increase. With C2 e C3 e 0.0068 mF the 2 dB steps take place at 130 Hz and 11.2 kHz. TL/H/11279 – 7 FIGURE 5. Loudness Control Circuit SERIAL DATA COMMUNICATION The LMC1983 uses the INTERMETAL serial bus (IM Bus) standard. Serial data information is sent to the LMC1983 over a three wire IM Bus consisting of Clock (CLK), Data (DATA), and Identity (ID). The DATA line is bidirectional and the CLK and ID lines are unidirectional from the microprocessor or micontroller to the LMC1983. The LMC1983’s bidirectional capability is accomplished by using an open drain output on the DATA line and an external 1 kX pull-up resistor. The LMC1983 responds to address values from 01000000 (40H) through 01000111 (47H). The addresses select one of the eight available functions (see Table I). The IM Bus’ lines have a logic high standby state when using TTL logic levels. As shown in Figure 6 , data transmission is initiated by low levels on CLK and ID. Next, eight address bits are sent. This address information includes the code to select one of the LMC1983’s desired functions. Each address bit is clocked in on the rising edge of CLK. The ID line is taken high after the eight bits of address data are received by the LMC1983. LOUDNESS The human ear has less sensitivity to high and low frequencies relative to its sensitivity to mid-range frequencies between 2 kHz and 6 kHz for any given acoustic level. The low and high frequency sensitivity decreases faster than the sensitivity to the mid-range frequencies as the acoustic level drops. The LMC1983’s loudness function can be used to help compensate for the decreased sensitivity by boosting the gain at low and high frequencies as the volume control attenuation increases (see the curve labeled ‘‘Gain vs Frequency with Loudness Active’’). The LMC1983’s loudness function uses external components R1, R2, C4 and C5, as shown in Figure 5 , to select the frequencies where bass and treble boost begin. The amount TL/H/11279 – 8 FIGURE 6. LMC1983’s INTERMETAL Serial Bus Timing 10 Application Information (Continued) change a function’s operating point. CLK must be stopped when the final 8 data bits are received. The data stored in the internal data latch remains unchanged until the ID is pulsed, signifying the end of data transmission. When ID is pulsed, the new data in the data shift register is latched into the data latch and the selected function takes on a new operating point. A complete description and more information concerning the IM Bus is given in the appendix of ITT’s CCU2000 datasheet. The controlling system continues toggling the CLK line eight more times. Data that determines the selected function’s operating point is written into, or single bit information on DIGITAL INPUT 1 or DIGITAL INPUT 2 is read from, the LMC1983. Finally, the end of transmission is signaled by pulsing the ID line low for a minimum of 3 ms. The transmitted function data is latched and the function changes to its new setting. Table I also details the serial data structure, range, and bit assignments that sets each function’s operating point. The volume and tone controls’ function control data binarily increments from zero to maximum as the function’s operating point changes from 80 dB attenuation to 0 dB attenuation (volume) or b12 dB to a 12 dB (tone controls). Note that not all data bits are needed by each function. The extra bits shown as ‘‘X’’s (‘‘don’t cares’’) are position holders and have no affect on a respective control. They are necessary to properly position the data in the LMC1983’s internal data shift register. Unexpected results may take place if these bits are not sent. The LMC1983’s internal data shift register can handle either a 16-bit word or two 8-bit serial data transmissions. It is the final 8 bits of data received before the ID line goes high that are used as the LMC1983 selection and function addresses. The final eight bits after the ID line returns high are used to DIGITAL I/O The LMC1983’s two Digital Input pins, 2 and 3, provide single-bit communication between a peripheral device and the controller over the IM Bus. Each pin has an internal 30 kX pull-up resistor. Therefore, these pins should be connected to open collector/drain outputs. The type of information that could be received on these lines and retrieved by a controller include FM stereo pilot indication, power on/off, Secondary Audio Program (SAP), etc. According to Table I, the logic state of DIGITAL INPUT 1 and DIGITAL INPUT 2 is latched and can be retrieved over the IM Bus using the read command (47H). The single-bit information sent on the IM Bus is active low since these lines are internally pulled high. 11 LMC1983 Digitally-Controlled Stereo Tone and Volume Circuit with Three Selectable Stereo Inputs Physical Dimensions inches (millimeters) Order Number LMC1983CIN NS Package Number N28B Order Number LMC1983CIV NS Package Number V28A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 2900 Semiconductor Drive P.O. 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