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ISO2-CMOS MT8880C/MT8880C-1 Integrated DTMF Transceiver
Features
* * * * * * * Complete DTMF transmitter/receiver Central office quality Low power consumption Microprocessor port Adjustable guard time Automatic tone burst mode Call progress mode
ISSUE 2
May 1995
Ordering Information MT8880CE/CE-1 20 Pin Plastic DIP MT8880CC/CC-1 20 Pin Ceramic DIP MT8880CS/CS-1 20 Pin SOIC MT8880CN/CN-1 24 Pin SSOP MT8880CP/CP-1 28 Pin Plastic LCC -40C to +85C based upon the industry standard MT8870 monolithic DTMF receiver; the transmitter utilizes a switched capacitor D/A converter for low distortion, high accuracy DTMF signalling. Internal counters provide a burst mode such that tone bursts can be transmitted with precise timing. A call progress filter can be selected allowing a microprocessor to analyze call progress tones. A standard microprocessor bus is provided and is directly compatible with 6800 series microprocessors. The MT8880C-1 is functionally identical to the MT8880C except for the performance of the receiver section, which is enhanced to accept and reject lower signal levels.
Applications
* * * * * Credit card systems Paging systems Repeater systems/mobile radio Interconnect dialers Personal computers
Description
The MT8880C/C-1 is a monolithic DTMF transceiver with call progress filter. It is fabricated in Mitel's ISO2-CMOS technology, which provides low power dissipation and high reliability. The DTMF receiver is
TONE
D/A Converters
Row and Column Counters
Transmit Data Register Status Register
Data Bus Buffer
D0 D1 D2 D3
Tone Burst Gating Cct. IN+ INGS OSC1 OSC2 Oscillator Circuit Bias Circuit VDD VRef VSS + Dial Tone Filter
Control Logic
Interrupt Logic IRQ/CP
High Group Filter Low Group Filter Control Logic
Digital Algorithm and Code Converter
Control Register A Control Register B I/O Control
2 CS R/W RS0
Steering Logic
Receive Data Register
ESt
St/GT
Figure 1 - Functional Block Diagram
4-33
MT8880C/MT8880C-1
ISO2-CMOS
GS NC ININ+ VDD St/GT EST
20 PIN CERDIP/PLASTIC DIP/SOIC
24 PIN SSOP
Figure 2 - Pin Connections
Pin Description
Pin # 20 24 28 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 1 2 4 6 7 Name IN+ Non-inverting op-amp input. INGS Inverting op-amp input. Gain Select. Gives access to output of front end differential amplifier for connection of feedback resistor. Description
VRef Reference Voltage output, nominally VDD/2 is used to bias inputs at mid-rail (see Fig. 13). VSS Ground input (0V).
8 OSC1 DTMF clock/oscillator input. 9 OSC2 Clock output. A 3.579545 MHz crystal connected between OSC1 and OSC2 completes the internal oscillator circuit. Leave open circuit when OSC1 is clock input. R/W Read/Write input. Controls the direction of data transfer to and from the MPU and the transceiver registers. TTL compatible. CS 2 Chip Select, TTL input (CS=0 to select the chip). System Clock input. TTL compatible. N.B. 2 clock input need not be active when the device is not being accessed. RS0 Register Select input. See register decode table. TTL compatible.
10 12 TONE Tone output (DTMF or single tone). 11 13
10 12 14 11 13 15 12 14 17
13 15 18 IRQ/ Interrupt Request to MPU (open drain output). Also, when call progress (CP) mode has CP been selected and interrupt enabled the IRQ/CP pin will output a rectangular wave signal representative of the input signal applied at the input op-amp. The input signal must be within the bandwidth limits of the call progress filter. See Figure 8. 14- 18- 19- D0-D3 Microprocessor Data Bus (TTL compatible). High impedance when CS = 1 or 2 is low. 17 21 22 18 22 26 ESt Early Steering output. Presents a logic high once the digital algorithm has detected a valid tone pair (signal condition). Any momentary loss of signal condition will cause ESt to return to a logic low.
19 23 27 St/GT Steering Input/Guard Time output (bidirectional). A voltage greater than VTSt detected at St causes the device to register the detected tone pair and update the output latch. A voltage less than VTSt frees the device to accept a new tone pair. The GT output acts to reset the external steering time-constant; its state is a function of ESt and the voltage on St. 20 24 28
8,9 16, 17
VDD Positive power supply input (+5V typical). NC No Connection.
3,5, 10, 11, 16, 2325
4-34
TONE R/W CS RS0 NC 2 IRQ/CP
IN+ INGS VRef VSS OSC1 OSC2 TONE R/W CS
1 2 3 4 5 6 7 8 9 10
20 19 18 17 16 15 14 13 12 11
VDD St/GT ESt D3 D2 D1 D0 IRQ/CP 2 RS0
IN+ INGS VRef VSS OSC1 OSC2 NC NC TONE R/W CS
1 2 3 4 5 6 7 8 9 10 11 12
24 23 22 21 20 19 18 17 16 15 14 13
VDD St/GT ESt D3 D2 D1 D0 NC NC IRQ/CP 2 RS0
4 3 2 1 28 27 26
*
12 13 14 15 16 17 18
NC VRef VSS OSC1 OSC2 NC NC
5 6 7 8 9 10 11
25 24 23 22 21 20 19
NC NC NC D3 D2 D1 D0
28 PIN PLCC
ISO2-CMOS
Functional Description
The MT8880C/C-1 Integrated DTMF Transceiver architecture consists of a high performance DTMF receiver with internal gain setting amplifier and a DTMF generator which employs a burst counter such that precise tone bursts and pauses can be synthesized. A call progress mode can be selected such that frequencies within the specified passband can be detected. A standard microprocessor interface allows access to an internal status register, two control registers and two data registers.
MT8880C/MT8880C-1
C1
R1
IN+
INC2 R4 R5 GS R3 R2 VRef MT8880C/C-1 DIFFERENTIAL INPUT AMPLIFIER C1 = C2 = 10 nF R1 = R4 = R5 = 100 k R2 = 60k, R3 = 37.5 k R3 = (R2R5)/(R2 + R5) VOLTAGE GAIN (AV diff) = R5/R1 INPUT IMPEDANCE (ZINdiff) = 2 R12 + (1/C)2
Input Configuration
The input arrangement of the MT8880C/C-1 provides a differential-input operational amplifier as well as a bias source (VRef) which is used to bias the inputs at VDD/2. Provision is made for connection of a feedback resistor to the op-amp output (GS) for adjustment of gain. In a single-ended configuration, the input pins are connected as shown in Figure 3. Figure 4 shows the necessary connections for a differential input configuration.
Figure 4 - Differential Input Configuration which are provided with hysteresis to prevent detection of unwanted low-level signals. The outputs of the comparators provide full rail logic swings at the frequencies of the incoming DTMF signals. Following the filter section is a decoder employing digital counting techniques to determine the frequencies of the incoming tones and to verify that they correspond to standard DTMF frequencies. A complex averaging algorithm protects against tone simulation by extraneous signals such as voice while providing tolerance to small frequency deviations and variations. This averaging algorithm has been developed to ensure an optimum combination of immunity to talk-off and tolerance to the presence of interfering frequencies (third tones) and noise. When the detector recognizes the presence of two valid tones (this is referred to as the "signal condition" in some industry specifications) the "Early Steering" (ESt) output will go to an active state. Any subsequent loss of signal condition will cause ESt to assume an inactive state.
IN+
C
RIN
IN-
RF
GS
VRef VOLTAGE GAIN (AV) = RF / RIN MT8880C/C-1
Figure 3 - Single-Ended Input Configuration
Receiver Section
Separation of the low and high group tones is achieved by applying the DTMF signal to the inputs of two sixth-order switched capacitor bandpass filters, the bandwidths of which correspond to the low and high group frequencies (see Fig. 7). These filters also incorporate notches at 350 Hz and 440 Hz for exceptional dial tone rejection. Each filter output is followed by a single order switched capacitor filter section which smooths the signals prior to limiting. Limiting is performed by high-gain comparators
4-35
MT8880C/MT8880C-1
Steering Circuit
ISO2-CMOS
Guard Time Adjustment
The simple steering circuit shown in Figure 5 is adequate for most applications. Component values are chosen according to the formula:
Before registration of a decoded tone pair, the receiver checks for a valid signal duration (referred to as character recognition condition). This check is performed by an external RC time constant driven by ESt. A logic high on ESt causes vc (see Figure 5) to rise as the capacitor discharges. Provided that the signal condition is maintained (ESt remains high) for the validation period (t GTP), v c reaches the threshold (V TSt) of the steering logic to register the tone pair, latching its corresponding 4-bit code (see Figure 7) into the Receive Data Register. At this point the GT output is activated and drives v c to V DD. GT continues to drive high as long as ESt remains high. Finally, after a short delay to allow the output latch to settle, the delayed steering output flag goes high, signalling that a received tone pair has been registered. The status of the delayed steering flag can be monitored by checking the appropriate bit in the status register. If Interrupt mode has been the selected, the IRQ/CP pin will pull low when delayed steering flag is active. The contents of the output latch are updated on an active delayed steering transition. This data is presented to the four bit bidirectional data bus when the Receive Data Register is read. The steering circuit works in reverse to validate the interdigit pause between signals. Thus, as well as rejecting signals too short to be considered valid, the receiver will tolerate signal interruptions (drop out) too short to be considered a valid pause. This facility, together with the capability of selecting the steering time constants externally, allows the designer to tailor performance to meet a wide variety of system requirements.
tREC = tDP+t GTP tID=t DA+tGTA
The value of tDP is a device parameter (see AC Electrical Characteristics) and t REC is the minimum signal duration to be recognized by the receiver. A value for C1 of 0.1 F is recommended for most applications, leaving R1 to be selected by the designer. Different steering arrangements may be used to select independently the guard times for tone present (tGTP) and tone absent (tGTA). This may be necessary to meet system specifications which place both accept and reject limits on both tone duration and interdigital pause. Guard time adjustment also allows the designer to tailor system parameters such as talk off and noise immunity.
tGTP = (RPC1) In [VDD / (VDD-VTSt)] tGTA = (R1C1) In (VDD /VTSt)
VDD C1 St/GT
RP = (R1R2) / (R1 + R2)
R1 ESt
R2
a) decreasing tGTP; (tGTP < tGTA)
VDD
tGTP = (R1C1) In [VDD / (VDD-VTSt) tGTA = (RpC1) In (VDD /VTSt)
VDD St/GT ESt R1
C1
RP = (R1R2) / (R1 + R2)
Vc VDD C1 St/GT
tGTA = (R1C1) In (VDD / VTSt)
MT8880C/C-1
R1 ESt
R2
tGTP = (R1C1) In [VDD / (VDD-VTSt)]
b) decreasing tGTA; (tGTP > tGTA)
Figure 5 - Basic Steering Circuit
4-36
Figure 6 - Guard Time Adjustment
ISO2-CMOS
Increasing tREC improves talk-off performance since it reduces the probability that tones simulated by speech will maintain a valid signal condition long enough to be registered. Alternatively, a relatively short tREC with a long tDO would be appropriate for extremely noisy environments where fast acquisition time and immunity to tone drop-outs are required. Design information for guard time adjustment is shown in Figure 6. The receiver timing is shown in Figure 9 with a description of the events in Figure 11.
FLOW
MT8880C/MT8880C-1
FHIGH DIGIT D3 D2 D1 D0
697 697 697 770 770 770 852
1209 1336 1477 1209 1336 1477 1209 1336 1477 1336 1209 1477 1633 1633 1633 1633
1 2 3 4 5 6 7 8 9 0 * # A B C D
0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0
0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0
0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0
1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
Call Progress Filter
A call progress mode, using the MT8880C/C-1, can be selected allowing the detection of various tones which identify the progress of a telephone call on the network. The call progress tone input and DTMF input are common, however, call progress tones can only be detected when CP mode has been selected. DTMF signals cannot be detected if CP mode has been selected (see Table 5). Figure 8 indicates the useful detect bandwidth of the call progress filter. Frequencies presented to the input, which are within the `accept' bandwidth limits of the filter, are hardlimited by a high gain comparator with the IRQ/CP pin serving as the output. The squarewave output obtained from the schmitt trigger can be analyzed by a microprocessor or counter arrangement to determine the nature of the call progress tone being detected. Frequencies which are in the `reject' area will not be detected and consequently the IRQ/CP pin will remain low.
852 852 941 941 941 697 770 852 941
0= LOGIC LOW, 1= LOGIC HIGH
Figure 7 - Functional Encode/Decode Table
LEVEL (dBm)
DTMF Generator
The DTMF transmitter employed in the MT8880C/C1 is capable of generating all sixteen standard DTMF tone pairs with low distortion and high accuracy. All frequencies are derived from an external 3.579545 MHz crystal. The sinusoidal waveforms for the individual tones are digitally synthesized using row and column programmable dividers and switched capacitor D/A converters. The row and column tones are mixed and filtered providing a DTMF signal with low total harmonic distortion and high accuracy. To specify a DTMF signal, data conforming to the encoding format shown in Figure 7 must be written to the transmit Data Register. Note that this is the same as the receiver output code. The individual tones which are generated (fLOW and fHIGH) are referred to as Low Group and High Group tones. As seen from the table, the low group frequencies are 697, 770, 852 and 941 Hz. The high group frequencies are 1209, 1336, 1477 and 1633 Hz. Typically, the high group to low group amplitude ratio (pre-emphasis) is 2dB to compensate for high group attenuation on long loops.
-25
AAAAAAAAAAAAA AAAAAAAAAAAAA AAAAAAAAAAAAA AAAAAAAAAAAAA AAAAAAAAAAAAA
0 = Reject
250 500 FREQUENCY (Hz)
750
= May Accept AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA = Accept AAAAAAAAAA AAAAAAAAAA
Figure 8 - Call Progress Response The period of each tone consists of 32 equal time segments. The period of a tone is controlled by varying the length of these time segments. During write operations to the Transmit Data Register the 4 bit data on the bus is latched and converted to 2 of 8 coding for use by the programmable divider circuitry. This code is used to specify a time segment length which will ultimately determine the frequency of the tone. When the divider reaches the appropriate count, as determined by the input code, a reset pulse is issued and the counter starts again. The number
4-37
MT8880C/MT8880C-1
EVENTS tREC Vin tDP ESt A
ISO2-CMOS
B tREC TONE #n tID
C
D tDO TONE #n + 1
E
F
TONE #n + 1
tDA tGTP tGTA VTSt tPStRX
St/GT
RX0-RX3
DECODED TONE # (n-1)
#n tPStb3
# (n + 1)
b3
b2
Read Status Register IRQ/CP
Figure 9 - Receiver Timing Diagram of time segments is fixed at 32, however, by varying the segment length as described above the tone output signal frequency will be varied. The divider output clocks another counter which addresses the sinewave lookup ROM. The lookup table contains codes which are used by the switched capacitor D/A converter to obtain discrete and highly accurate DC voltage levels. Two identical circuits are employed to produce row and column tones which are then mixed using a low noise summing amplifier. The oscillator described needs no "start-up" time as in other DTMF generators since the crystal oscillator is running continuously thus providing a high degree of tone burst accuracy. A bandwidth limiting filter is incorporated and serves to attenuate distortion products above 8 kHz. It can be seen from Figure 10 that the distortion products are very low in amplitude.
Scaling Information 10 dB/Div Start Frequency = 0 Hz Stop Frequency = 3400 Hz Marker Frequency = 697 Hz and 1209 Hz
Figure 10 - Spectrum Plot
4-38
ISO2-CMOS
Burst Mode
In certain telephony applications it is required that DTMF signals being generated are of a specific duration determined either by the particular application or by any one of the exchange transmitter specifications currently existing. Standard DTMF signal timing can be accomplished by making use of the Burst Mode. The transmitter is capable of issuing symmetric bursts/pauses of predetermined duration. This burst/pause duration is 51 ms1 ms which is a standard interval for autodialer and central office applications. After the burst/pause has been issued, the appropriate bit is set in the Status Register indicating that the transmitter is ready for more data. The timing described above is available when DTMF mode has been selected. However, when CP mode (Call Progress mode) is selected, a second burst/ pause time of 102 ms 2 ms is available. This extended interval is useful when precise tone bursts of longer than 51 ms duration and 51 ms pause are desired. Note that when CP mode and Burst mode have been selected, DTMF tones may be transmitted only and not received. In applications where a non-standard burst/pause duration is required, burst mode must be disabled
MT8880C/MT8880C-1
and the transmitter gated on and off by an external hardware or software timer.
Single Tone Generation
A single tone mode is available whereby individual tones from the low group or high group can be generated. This mode can be used for DTMF test equipment applications, acknowledgment tone generation and distortion measurements. Refer to Control Register B description for details.
Distortion Calculations
The MT8880C/C-1 is capable of producing precise tone bursts with minimal error in frequency (see Table 1). The internal summing amplifier is followed by a first-order lowpass switched capacitor filter to minimize harmonic components and intermodulation products. The total harmonic distortion for a single tone can be calculated using Equation 1, which is the ratio of the total power of all the extraneous frequencies to the power of the fundamental frequency expressed as a percentage. The Fourier components of the tone output correspond to V2f.... Vnf as measured on the output waveform. The total harmonic distortion for a dual tone can be calculated
EXPLANATION OF EVENTS A) TONE BURSTS DETECTED, TONE DURATION INVALID, RX DATA REGISTER NOT UPDATED. B) TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER. C) END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER RETAINED UNTIL NEXT VALID TONE PAIR. D) TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER. E) ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, DATA REMAINS UNCHANGED. F) END OF TONE #n+1 DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER RETAINED UNTIL NEXT VALID TONE PAIR. EXPLANATION OF SYMBOLS DTMF COMPOSITE INPUT SIGNAL. Vin ESt EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES. St/GT STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT. RX0 -RX3 4-BIT DECODED DATA IN RECEIVE DATA REGISTER b3 DELAYED STEERING. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE REQUIRED GUARD TIME THUS CONSTITUTING A VALID SIGNAL. ACTIVE LOW FOR THE DURATION OF A VALID DTMF SIGNAL. b2 INDICATES THAT VALID DATA IS IN THE RECEIVE DATA REGISTER. THE BIT IS CLEARED AFTER THE STATUS REGISTER IS READ. IRQ/CP INTERRUPT IS ACTIVE INDICATING THAT NEW DATA IS IN THE RX DATA REGISTER. THE INTERRUPT IS CLEARED AFTER THE STATUS REGISTER IS READ. MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID. tREC MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION. tREC MINIMUM TIME BETWEEN VALID SEQUENTIAL DTMF SIGNALS. tID MAXIMUM ALLOWABLE DROPOUT DURING VALID DTMF SIGNAL. tDO TIME TO DETECT VALID FREQUENCIES PRESENT. tDP TIME TO DETECT VALID FREQUENCIES ABSENT. tDA GUARD TIME, TONE PRESENT. tGTP GUARD TIME, TONE ABSENT. tGTA
Figure 11 - Description of Timing Events
4-39
MT8880C/MT8880C-1
ISO2-CMOS
Maximum Series Resistance:150 ohms Maximum Drive Level: 2mW
V22f + V23f + V24f + .... V2nf
e.g.
THD(%) = 100 Vfundamental
CTS Knights MP036S Toyocom TQC-203-A-9S
Equation 1. THD (%) For a Single Tone
V22L + V23L + .... V2nL + V22H + V23H + .. V2nH + V2IMD THD (%) = 100 V2L + V2H
A number of MT8880C/C-1 devices can be connected as shown in Figure 12 such that only one crystal is required. Alternatively, the OSC1 inputs on all devices can be driven from a TTL buffer with the OSC2 outputs left unconnected.
MT8880C/C-1 OSC1 OSC2
MT8880C/C-1 OSC1 OSC2
MT8880C/C-1 OSC1 OSC2
Equation 2. THD (%) For a Dual Tone
OUTPUT FREQUENCY (Hz) SPECIFIED ACTUAL 3.579545 MHz %ERROR
ACTIVE INPUT
Figure 12 - Common Crystal Connection +0.30 -0.49 -0.54 +0.74 +0.57 -0.32 -0.35 +0.73 The Receive Data Register contains the output code of the last valid DTMF tone pair to be decoded and is a read only register. The data entered in the Transmit Data Register will determine which tone pair is to be generated (see Figure 7 for coding details). Data can only be written to the transmit register. Transceiver control is accomplished with two Control Registers (CRA and CRB) which occupy the same address space. A write operation to CRB can be executed by setting the appropriate bit in CRA. The following write operation to the same address will then be directed to CRB and subsequent write cycles will then be directed back to CRA. A software reset must be included at the beginning of all programs to initialize the control and status registers after power up or power reset (see Figure 16). Refer to Tables 3, 4, 5 and 6 for details concerning the Control Registers. The IRQ/CP pin can be programmed such that it will provide an interrupt request signal upon validation of DTMF signals or when the transmitter is ready for more data (Burst mode only). The IRQ/CP pin is configured as an open drain output device and as such requires a pull-up resistor (see Figure 13). The MT8880C/C-1 employs a microprocessor interface which allows precise control of transmitter and receiver functions. There are five internal registers associated with the microprocessor interface which can be subdivided into three categories, i.e., data transfer, transceiver control and transceiver status. There are two registers associated with data transfer operations.
L1 L2 L3 L4 H1 H2 H3 H4
697 770 852 941 1209 1336 1477 1633
699.1 766.2 847.4 948.0 1215.9 1331.7 1471.9 1645.0
Microprocessor Interface
Table 1. Actual Frequencies Versus Standard Requirements using Equation 2. V L and VH correspond to the low group amplitude and high group amplitude, respectively, and V2IMD is the sum of all the intermodulation components. The internal switchedcapacitor filter following the D/A converter keeps distortion products down to a very low level as shown in Figure 10.
DTMF Clock Circuit
The internal clock circuit is completed with the addition of a standard television colour burst crystal. The crystal specification is as follows: Frequency: Frequency Tolerance: Resonance Mode: Load Capacitance: 3.579545 MHz
0.1%
Parallel 18pF
4-40
ISO2-CMOS
MT8880C/MT8880C-1
b2 IRQ b1 CP/DTMF b0 TOUT
RS0 0 0 1 1
R/W 0 1 0 1
FUNCTION Write to Transmit Data Register Read from Receive Data Register Write to Control Register Read from Status Register
b3 RSEL
Table 3. CRA Bit Positions
b3 C/R
b2 S/D
b1 TEST
b0 BURST
Table 2. Internal Register Functions
Table 4. CRB Bit Positions
BIT b0 b1
NAME TOUT CP/DTMF
FUNCTION TONE OUTPUT MODE CONTROL
DESCRIPTION A logic `1' enables the tone output. This function can be implemented in either the burst mode or non-burst mode. In DTMF mode (logic `0') the device is capable of generating and receiving Dual Tone Multi-Frequency signals. When the CP (Call Progress) mode is selected (logic `1') a 6th order bandpass filter is enabled to allow call progress tones to be detected. Call progress tones which are within the specified bandwidth will be presented at the IRQ/CP pin in rectangular wave format if the IRQ bit has been enabled (b2=1). Also, when the CP mode and BURST mode have both been selected, the transmitter will issue DTMF signals with a burst and pause of 102 ms (typ) duration. This signal duration is twice that obtained from the DTMF transmitter if DTMF mode had been selected. Note that DTMF signals cannot be decoded when the CP mode of operation has been selected. A logic `1' enables the INTERRUPT mode. When this mode is active and the DTMF mode has been selected (b1=0) the IRQ/ CP pin will pull to a logic `0' condition when either 1) a valid DTMF signal has been received and has been present for the guard time duration or 2) the transmitter is ready for more data (BURST mode only). A logic `1' selects Control Register B on the next Write cycle to the Control Register address. Subsequent Write cycles to the Control Register are directed back to Control Register A.
b2
IRQ
INTERRUPT ENABLE
b3
RSEL
REGISTER SELECT
Table 5. Control Register A Description
4-41
MT8880C/MT8880C-1
BIT b0 NAME BURST FUNCTION BURST MODE
ISO2-CMOS
DESCRIPTION A logic `0' enables the burst mode. When this mode is selected, data corresponding to the desired DTMF tone pair can be written to the Transmit Register resulting in a tone burst of a specific duration (see AC Characteristics). Subsequently, a pause of the same duration is induced. Immediately following the pause, the Status Register is updated indicating that the Transmit Register is ready for further instructions and an interrupt will be generated if the interrupt mode has been enabled. Additionally, if call progress (CP) mode has been enabled, the burst and pause duration is increased by a factor of two. When the burst mode is not selected (logic `1') tone bursts of any desired duration may be generated. By enabling the test mode (logic'1'), the IRQ/CP pin will present the delayed steering (inverted) signal from the DTMF receiver. Refer to Figure 9 (b3 waveform) for details concerning the output waveform. DTMF mode must be selected (CRA b1=0) before test mode can be implemented. A logic `0' will allow Dual Tone Multi-Frequency signals to be produced. If single tone generation is enabled (logic `1'), either row or column tones (low group or high group) can be generated depending on the state of b3 in Control Register B. When used in conjunction with b2 (above) the transmitter can be made to generate single row or single column frequencies. A logic `0' will select row frequencies and a logic `1' will select column frequencies.
b1
TEST
TEST MODE
b2
S/D
SINGLE /DUAL TONE GENERATION
b3
C/R
COLUMN/ROW TONES
Table 6. Control Register B Description
BIT b0 b1
NAME IRQ TRANSMIT DATA REGISTER EMPTY (BURST MODE ONLY) RECEIVE DATA REGISTER FULL DELAYED STEERING
STATUS FLAG SET Interrupt has occurred. Bit one (b1) or bit two (b2) is set. Pause duration has terminated and transmitter is ready for new data. Valid data is in the Receive Data Register. Set upon the valid detection of the absence of a DTMF signal.
STATUS FLAG CLEARED Interrupt is inactive. Cleared after Status Register is read. Cleared after Status Register is read or when in non-burst mode. Cleared after Status Register is read. Cleared upon the detection of a valid DTMF signal.
b2 b3
Table 7. Status Register Description
4-42
ISO2-CMOS
MT8880C/MT8880C-1
VDD
MT8880C/C-1 C1 DTMF/CP INPUT R2 R1 IN+ INGS VRef VSS X-tal OSC1 OSC2 DTMF OUTPUT TONE C4 RL R/W CS VDD St/GT ESt D3 D2 D1 D0 IRQ/CP 2 RS0 R3 C2
C3
R4
To P or C
Notes: R1, R2 = 100 k 1% R3 = 374 1% R4 = 3.3 k 10% RL = 10 k (min.) C1 = 100 nF 5% C2 = 100 nF 5% C3 = 100 nF 10%* C4 = 10 nF 10% X-tal = 3.579545 MHz
* Microprocessor based systems can inject undesirable noise into the supply rails. The performance of the MT8880 can be optimized by keeping noise on the supply rails to a minimum. The decoupling capacitor (C3) should be connected close to the device and ground loops should be avoided.
Figure 13 - Application Circuit (Single-Ended Input)
5.0 VDC MMD6150 (or equivalent) 2.4 k
5.0 VDC TEST POINT 3 k
TEST POINT
130 pF
24 k MMD7000 (or equivalent)
70 pF
Test load for D0-D3 pins
Test load for IRQ/CP pin
Figure 14 - Test Circuit
4-43
MT8880C/MT8880C-1
ISO2-CMOS
+5V 6802 IRQ 3.3k MT8880C/C-1 IRQ RS0
Address Peripheral decode CS
VMA R/W E Data R/W 2 Data
Figure 15 - MT8880C/C-1 to 6802 Interface
EXAMPLE 1: A software reset must be included at the beginning of all programs to initialize the control registers after power up. The initialization procedure should be implemented 100ms after power up. Description Control Data RS0 R/W b3 b2 b1 b0 CS 1) Read Status Register 0 1 1 X X X X 2) Write to Control Register 0 1 0 0 0 0 0 3) Write to Control Register 0 1 0 0 0 0 0 4) Write to Control Register 0 1 0 1 0 0 0 5) Write to Control Register 0 1 0 0 0 0 0 6) Read Status Register 0 1 1 X X X X EXAMPLE 2: Transmit DTMF tones of 50 ms burst/50 ms pause and Receive DTMF Tones Description RS0 R/W b3 b2 b1 b0 CS 1) Write to Control Register A 0 1 0 1 1 0 1 (tone out, DTMF, IRQ, Select Control Register B) 2) Write to Control Register B 0 1 0 0 0 0 0 (burst mode) 3) Write to Transmit Data Register 0 0 0 0 1 1 1 (send a digit 7) --------------------------------------wait for an interrupt or poll Status Register ---------------------------------------------4) Read the Status Register 0 1 1 X X X X -if bit 1 is set, the Tx is ready for the next tone, in which case... Write to Transmit Register 0 0 0 (send a digit 5) -if bit 2 is set, a DTMF tone has been received, in which case.... Read the Receive Data Register 0 0 1 -if both bits are set... Read the Receive Data Register Write to Transmit Data Register
0
1
0
1
X
X
X
X
0 0
0 0
1 0
X 0
X 1
X 0
X 1
NOTE: IN THE TX BURST MODE, STATUS REGISTER BIT 1 WILL NOT BE SET UNTIL 100 ms (2 ms) AFTER THE DATA IS WRITTEN TO THE TX DATA REGISTER. IN EXTENDED BURST MODE THIS TIME WILL BE DOUBLED TO 200 ms ( 4 ms).
Figure 16 - Application Hints
4-44
ISO2-CMOS
Absolute Maximum Ratings*
Parameter 1 2 3 4 5 Power supply voltage VDD-VSS Voltage on any pin Current at any pin (Except VDD and VSS) Storage temperature Package power dissipation Symbol VDD VI TST PD
MT8880C/MT8880C-1
Min
Max 6
Units V V mA C mW
VSS-0.3 -65
VDD+0.3 10 +150 1000
* Exceeding these values may cause permanent damage. Functional operation under these conditions is not implied.
Recommended Operating Conditions - Voltages are with respect to ground (VSS) unless otherwise stated.
Parameter 1 2 Positive power supply Operating temperature Sym VDD TO Min 4.75 -40 Typ 5.00 Max 5.25 +85 Units V C Test Conditions
3 Crystal clock frequency fCLK 3.575965 3.579545 3.583124 MHz Typical figures are at 25 C and for design aid only: not guaranteed and not subject to production testing.
DC Electrical Characteristics - VSS=0 V.
Characteristics 1 2 3 4 5 6 7 8 9 10 11 12 13 14
D i g i t a l Data Bus ESt and St/Gt IRQ/ CP O U T P U T S S U P I N P U T S
Sym VDD IDD PC VIHO VILO VTSt VOLO VOHO IOZ VRef ROR VIL VIH IIZ
Min 4.75
Typ 5.0 7.0
Max 5.25 11 57.8
Units V mA mW V
Test Conditions
Operating supply voltage Operating supply current Power consumption High level input voltage (OSC1) Low level input voltage (OSC1) Steering threshold voltage Low level output voltage (OSC2) High level output voltage (OSC2) Output leakage current (IRQ) VRef output voltage VRef output resistance Low level input voltage High level input voltage Input leakage current
3.5 1.5 2.2 2.3 2.5 0.1 4.9 1 2.4 2.5 1.3 0.8 2.0 10 10 2.6
V V V V A V k V V A VIN=VSS to VDD No load VDD=5 V VOH=2.4 V No load, VDD=5V VDD=5V No load
15 16 17 18 19
Source current Sink current Source current Sink current Sink current
IOH IOL IOH IOL IOL
-1.4 2.0 -0.5 2 4
-6.6 4.0 -3.0 4 16
mA mA mA mA mA
VOH=2.4V VOL=0.4V VOH=4.6V VOL=0.4V VOL=0.4V
Characteristics are over recommended operating conditions unless otherwise stated. Typical figures are at 25 C, VDD =5V and for design aid only: not guaranteed and not subject to production testing.
4-45
MT8880C/MT8880C-1
ISO2-CMOS
Electrical Characteristics Gain Setting Amplifier - Voltages are with respect to ground (VSS) unless otherwise stated, VSS= 0 V, VDD=5V, TO=25C.
Characteristics 1 2 3 4 5 6 7 8 9 10 11 Input leakage current Input resistance Input offset voltage Power supply rejection Common mode rejection DC open loop voltage gain Unity gain bandwidth Output voltage swing Allowable capacitive load (GS) Allowable resistive load (GS) Common mode range Sym IIN RIN VOS PSRR CMRR AVOL BW VO CL RL VCM Min Typ 100 10 25 60 60 65 1.5 4.5 100 50 3.0 Max Units nA M mV dB dB dB MHz Vpp pF k Vpp No Load RL 100 k to VSS 1 kHz 0.75V VIN 4.25V Test Conditions VSS VIN VDD
Typical figures are at 25C and for design aid only: not guaranteed and not subject to production testing.
MT8880C-1 AC Electrical Characteristics - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics Valid input signal levels (each tone of composite signal) R X 2 Input Signal Level Reject -37 Sym Min -31 21.8 +1 869 Typ Max Units dBm mVRMS dBm mVRMS dBm Notes* 1,2,3,5,6,9 1,2,3,5,6,9 1,2,3,5,6,9 1,2,3,5,6,9 1,2,3,5,6,9 1,2,3,5,6,9
1
10.9 mVRMS Characteristics are over recommended temperature and at VDD=5V, using the test circuit shown in Figure 13. Typ
MT8880C AC Electrical Characteristics- Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics Valid Input signal levels (each tone of composite signal) Sym Min -29 1 R X 27.5 +1 Max Units dBm mVRMS dBm Notes* 1,2,3,5,6,9 1,2,3,5,6,9 1,2,3,5,6,9
1,2,3,5,6,9 869 mVRMS Characteristics are over recommended operating conditions (unless otherwise stated) using the test circuit shown in Figure 13.
AC Electrical Characteristics - Voltages are with respect to ground (VSS) unless otherwise stated. fC=3.579545 MHz.
Characteristics 1 2 3 4 5 6 7 R X Positive twist accept Negative twist accept Freq. deviation accept Freq. deviation reject Third tone tolerance Noise tolerance Dial tone tolerance 1.5%2Hz 3.5% -16 -12 22 dB dB dB Sym Min Typ Max 8 8 Units dB dB Notes* 2,3,6,9 2,3,6,9 2,3,5,9 2,3,5 2,3,4,5,9,10 2,3,4,5,7,9,10 2,3,4,5,8,9,11
Characteristics are over recommended operating conditions unless otherwise stated. Typical figures are at 25C, VDD = 5V, and for design aid only: not guaranteed and not subject to production testing. * See "Notes" following AC Electrical Characteristics Tables.
4-46
ISO2-CMOS
MT8880C/MT8880C-1
AC Electrical Characteristics - Call Progress - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics 1 2 3 4 5 Lower freq. (ACCEPT) Upper freq. (ACCEPT) Lower freq. (REJECT) Upper freq. (REJECT) Call progress tone detect level (total power) Sym fLA fHA fLR fHR -30 Min Typ 320 510 290 540 Max Units Hz Hz Hz Hz dBm Notes* @ -25 dBm @ -25 dBm @ -25 dBm @ -25 dBm
Characteristics are over recommended operating conditions unless otherwise stated Typical figures are at 25C, VDD = 5V, and for design aid only: not guaranteed and not subject to production testing * See "Notes" AC Electrical Characteristics Tables
AC Electrical Characteristics - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
M P U I N T E R F A C E T O N E O U T T X R X
Sym tDP tDA tREC tREC tID tDO tPStb3 tPStRX tBST tPS tBSTE tPSE VHOUT VLOUT dBP THD fD RLT tCYC tCH tCL tR, tF tAH,tRWH tAS,tRWS tDHR tDDR tDSW
Min 3 0.5
Typ 11 4
Max 14 8.5 40
Units ms ms ms ms
Conditions Note 12 Note 12 User adjustable# User adjustable# User adjustable# User adjustable#
Tone present detect time Tone absent detect time Tone duration accept Tone duration reject Interdigit pause accept Interdigit pause reject Delay St to b3 Delay St to RX0-RX3 Tone burst duration Tone pause duration Tone burst duration (extended) Tone pause duration (extended) High group output level Low group output level Pre-emphasis Output distortion (Single Tone) Frequency deviation Output load resistance 2 cycle period 2 high pulse width 2 low pulse width 2 rise and fall time Address, R/W hold time Address, R/W setup time (before 2) Data hold time (read) 2 to valid data delay (read) Data setup time (write)
20 40 20 13 8 50 50 100 100 -6.1 -8.1 2 -35 0.7 10 250 115 110 25 26 23 22 100 45 1.5 50 52 52 104 104 -2.1 -4.1 3
ms ms s s ms ms ms ms dBm dBm dB dB % k ns ns ns ns ns ns ns ns ns
DTMF mode DTMF mode Call Progress mode Call Progress mode RL=10k RL=10k RL=10k 25 kHz Bandwidth RL=10k fC=3.579545 MHz
* 200 pF load
4-47
MT8880C/MT8880C-1
ISO2-CMOS
AC Electrical Characteristics (Cont`d) - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics 28 29 30 31 32 33 34
D T M F C L K
Sym tDHW CIN C OUT fC tLHCL tHLCL DCCL
Min 10
Typ
Max
Units ns
Notes*
Data hold time (write) Input Capacitance (data bus) Output Capacitance (IRQ/CP) Crystal/clock frequency Clock input rise time Clock input duty cycle Clock input duty cycle
5 5 3.5759 3.5795 3.5831 110 110 40 50 60
pF pF MHz ns ns % pF Ext. clock Ext. clock Ext. clock
35 Capacitive load (OSC2) CLO 30 Timing is over recommended temperature & power supply voltages. Typical figures are at 25C and for design aid only: not guaranteed and not subject to production testing. * The data bus output buffers are no longer sourcing or sinking current by tDHR. # See Figure 6 regarding guard time adjustment.
NOTES: 1) dBm=decibels above or below a reference power of 1 mW into a 600 ohm load. 2) Digit sequence consists of all 16 DTMF tones. 3) Tone duration=40 ms. Tone pause=40 ms. 4) Nominal DTMF frequencies are used. 5) Both tones in the composite signal have an equal amplitude. 6) The tone pair is deviated by 1.5%2 Hz. 7) Bandwidth limited (3 kHz) Gaussian noise. 8) The precise dial tone frequencies are 350 and 440 Hz (2%). 9) For an error rate of less than 1 in 10,000. 10) Referenced to the lowest amplitude tone in the DTMF signal. 11) Referenced to the minimum valid accept level. 12) For guard time calculation purposes.
4-48
ISO2-CMOS
MT8880C/MT8880C-1
tCYC tR 2 tCH tCL tF
Figure 17 - 2 Pulse
2 tAS CS tDDR tAH
RS0
tRWS
tRWH
R/W
tDHR
DATA BUS
Valid Data
Figure 18 - MPU Read Cycle
2 tAS CS tAH
RS0 tRWS R/W tDSW DATA BUS tDHW tRWH
Valid Data
Figure 19 - MPU Write Cycle
4-49
MT8880C/MT8880C-1
NOTES:
ISO2-CMOS
4-50

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