MT8888C
Integrated DTMF Transceiver
with Intel Micro Interface
Data Sheet
Features
September 2005
•
Central office quality DTMF transmitter/receiver
•
Low power consumption
•
High speed Intel micro interface
•
Adjustable guard time
•
Automatic tone burst mode
•
Call progress tone detection to -30 dBm
Ordering Information
MT8888CE
20 Pin PDIP
MT8888CS
20 Pin SOIC
MT8888CN
24 Pin SSOP
MT8888CP
28 Pin PLCC
MT8888CE1
20 Pin PDIP*
MT8888CS1
20 Pin SOIC*
MT8888CN1
24 Pin SSOP*
MT8888CP1
28 Pin PLCC*
MT8888CPR
28 Pin PLCC
MT8888CSR
20 Pin SOIC
MT8888CSR1 20 Pin SOIC*
MT8888CPR1 28 Pin PLCC*
*Pb Free Matte Tin
Applications
•
Credit card systems
•
Paging systems
•
Repeater systems/mobile radio
•
Interconnect dialers
•
Personal computers
The receiver section is based upon the industry
standard MT8870 DTMF receiver while 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.
The MT8888C is a monolithic DTMF transceiver with
call progress filter. It is fabricated in CMOS technology
offering low power consumption and high reliability.
Tone Burst
Gating Cct.
IN+
+
IN-
-
Dial
Tone
Filter
High Group
Filter
OSC2
Low Group
Filter
Oscillator
Circuit
Control
Logic
Bias
Circuit
VDD VRef
VSS
Transmit Data
Register
Status
Register
Control
Logic
GS
OSC1
The MT8888C utilizes an Intel micro interface, which
allows the device to be connected to a number of
popular microcontrollers with minimal external logic.
Row and
Column
Counters
D/A
Converters
∑
Reel
Reel
Reel
Reel
-40°C to +85°C
Description
TONE
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tape &
Tape &
Tape &
Tape &
Data
Bus
Buffer
D0
D1
D2
D3
Interrupt
Logic
IRQ/CP
Digital
Algorithm
and Code
Converter
Steering
Logic
ESt
Control
Register
A
Control
Register
B
RD
I/O
Control
Receive Data
Register
St/GT
Figure 1 - Functional Block Diagram
1
Zarlink Semiconductor Inc.
Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.
Copyright 2003-2005, Zarlink Semiconductor Inc. All Rights Reserved.
CS
WR
RS0
MT8888C
24
23
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
9
10
11
12
VDD
St/GT
ESt
D3
D2
D1
D0
NC
NC
IRQ/CP
RD
RS0
24 PIN SSOP
20 PIN PLASTIC DIP/SOIC
GS
NC
ININ+
VDD
St/GT
EST
IN+
INGS
VRef
VSS
OSC1
OSC2
NC
NC
TONE
WR
CS
4
3
2
1
28
27
26
VDD
St/GT
ESt
D3
D2
D1
D0
IRQ/CP
RD
RS0
NC
VRef
VSS
OSC1
OSC2
NC
NC
5
6
7
8
9
10
11
•
12
13
14
15
16
17
18
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
25
24
23
22
21
20
19
NC
NC
NC
D3
D2
D1
D0
TONE
WR
CS
RSO
NC
RD
IRQ/CP
IN+
INGS
VRef
VSS
OSC1
OSC2
TONE
WR
CS
Data Sheet
28 PIN PLCC
Figure 2 - Pin Connections
Pin Description
Pin #
20
24
28
Name
1
1
1
IN+
Non-inverting op-amp input.
2
2
2
IN-
Inverting op-amp input.
3
3
4
GS
Gain Select. Gives access to output of front end differential amplifier for
connection of feedback resistor.
4
4
6
VRef
Reference Voltage output (VDD/2).
5
5
7
VSS
Ground (0V ).
6
6
8
OSC1 DTMF clock/oscillator input. Connect a 4.7 MΩ resistor to VSS if crystal oscillator is
used.
7
7
9
OSC2 Oscillator output. A 3.579545 MHz crystal connected between OSC1 and OSC2
completes the internal oscillator circuit. Leave open circuit when OSC1 is driven
externally.
8
10
12
TONE Output from internal DTMF transmitter.
9
11
13
WR
Write microprocessor input. TTL compatible.
10
12
14
CS
Chip Select input. Active Low. This signal must be qualified externally by address
latch enable (ALE) signal, see Figure 14.
11
13
15
RS0
Register Select input. Refer to Table 3 for bit interpretation. TTL compatible.
12
14
17
RD
Read microprocessor input. TTL compatible.
13
15
18
14-17 18-21 19-22
Description
IRQ/CP Interrupt Request/Call Progress (open drain) output. In interrupt mode, this
output goes low when a valid DTMF tone burst has been transmitted or received.
In call progress mode, this pin will output a rectangular 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.
D0-D3 Microprocessor Data Bus. High impedance when CS = 1 or RD = 1.
TTL compatible.
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
Pin Description (continued)
Pin #
20
24
28
Name
18
22
26
ESt
19
23
27
St/GT
20
24
28
VDD
Positive power supply (5 V typical).
NC
No Connection.
8, 9, 3,5,10,
16,17 11,16,
23,25
1.0
Description
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.
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.
Functional Description
The MT8888C Integrated DTMF Transceiver consists of a high performance DTMF receiver with an internal gain
setting amplifier and a DTMF generator which employs a burst counter to synthesize precise tone bursts and
pauses. A call progress mode can be selected so that frequencies within the specified passband can be detected.
The Intel micro interface allows microcontrollers, such as the 8080, 80C31/51 and 8085, to access the MT8888C
internal registers.
2.0
Input Configuration
The input arrangement of the MT8888C 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 opamp output (GS) for gain adjustment. 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.
3.0
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 Table 1). These filters 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 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.
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
IN+
IN-
RIN
C
RF
GS
VRef
MT8888C
VOLTAGE GAIN
(AV) = RF / RIN
Figure 3 - Single-Ended Input Configuration
C1
R1
IN+
INC2
R4
R5
GS
R2
R3
VRef
MT8888C
DIFFERENTIAL INPUT AMPLIFIER
C1 = C2 = 10 nF
R1 = R4 = R5 = 100 kΩ
R2 = 60kΩ, R3 = 37.5 kΩ
R3 = (R2R5)/(R2 + R5)
VOLTAGE GAIN
(AV diff) - R5/R1
INPUT IMPEDANCE
(ZINdiff) = 2 R12 + (1/ωC)2
Figure 4 - Differential Input Configuration
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
FLOW
FHIGH
DIGIT
D3
D2
D1
D0
697
1209
1
0
0
0
1
697
1336
2
0
0
1
0
697
1477
3
0
0
1
1
770
1209
4
0
1
0
0
770
1336
5
0
1
0
1
770
1477
6
0
1
1
0
852
1209
7
0
1
1
1
852
1336
8
1
0
0
0
852
1477
9
1
0
0
1
941
1336
0
1
0
1
0
941
1209
*
1
0
1
1
941
1477
#
1
1
0
0
697
1633
A
1
1
0
1
770
1633
B
1
1
1
0
852
1633
C
1
1
1
1
941
1633
D
0
0
0
0
Table 1 - Functional Encode/Decode Table
Note: 0= LOGIC LOW, 1= LOGIC HIGH
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.
4.0
Steering Circuit
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 (tGTP), vc reaches the threshold (VTSt) of the steering logic to register the
tone pair, latching its corresponding 4-bit code (see Table 1) into the Receive Data Register. At this point the GT
output is activated and drives vc to VDD. 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 selected, the IRQ/CP pin will pull low when the 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
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
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.
VDD
MT8888C
C1
VDD
Vc
St/GT
ESt
R1
tGTA = (R1C1) In (VDD / VTSt)
tGTP = (R1C1) In [VDD / (VDD-VTSt)]
Figure 5 - Basic Steering Circuit
5.0
Guard Time Adjustment
The simple steering circuit shown in Figure 5 is adequate for most applications. Component values are chosen
according to the following inequalities (see Figure 7):
tREC ≥ tDPmax+tGTPmax - tDAmin
tREC ≤ tDPmin+tGTPmin - tDAmax
tID ≥ tDAmax+tGTAmax - tDPmin
tDO ≤ tDAmin+tGTAmin - tDPmax
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
tGTP = (RPC1) In [VDD / (VDD-VTSt)]
tGTA = (R1C1) In (VDD/VTSt)
RP = (R1R2) / (R1 + R2)
VDD
C1
St/GT
R1
ESt
R2
a) decreasing tGTP; (tGTP < tGTA)
tGTP = (R1C1) In [VDD / (VDD-VTSt)]
tGTA = (RpC1) In (VDD/VTSt)
RP = (R1R2) / (R1 + R2)
VDD
C1
St/GT
R1
R2
ESt
b) decreasing tGTA; (tGTP > tGTA)
Figure 6 - Guard Time Adjustment
The value of tDP is a device parameter (see AC Electrical Characteristics) and tREC is the minimum signal duration
to be recognized by the receiver. A value for C1 of 0.1 µF is recommended for most applications, leaving R1 to be
selected by the designer. Different steering arrangements may be used to select independent tone present (tGTP)
and tone absent (tGTA) guard times. This may be necessary to meet system specifications which place both accept
and reject limits on tone duration and interdigital pause. Guard time adjustment also allows the designer to tailor
system parameters such as talk off and noise immunity.
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 7 with a description of the events in Figure 9.
6.0
Call Progress Filter
A call progress mode, using the MT8888C, 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 7). 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
hard-limited 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.
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Zarlink Semiconductor Inc.
MT8888C
EVENTS
A
Data Sheet
B
C
tREC
tREC
D
F
tDO
tID
TONE
#n + 1
TONE #n
Vin
E
TONE
#n + 1
tDA
tDP
ESt
tGTP
tGTA
VTSt
St/GT
tPStRX
RX0-RX3
DECODED TONE # (n-1)
# (n + 1)
#n
tPStb3
b3
b2
Read
Status
Register
IRQ/CP
Figure 7 - Receiver Timing Diagram
LEVEL
(dBm)
-25
0
250
= Reject
500
750
FREQUENCY (Hz)
= May Accept
= Accept
Figure 8 - Call Progress Response
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
EXPLANATION OF EVENTS
A)
B)
C)
TONE BURSTS DETECTED, TONE DURATION INVALID, RX DATA REGISTER NOT UPDATED.
TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER
RETAINED UNTIL NEXT VALID TONE PAIR.
TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, DATA REMAINS UNCHANGED.
END OF TONE #n+1 DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER
RETAINED UNTIL NEXT VALID TONE PAIR.
D)
E)
F)
EXPLANATION OF SYMBOLS
Vin
ESt
St/GT
RX 0 -RX3
b3
b2
IRQ/CP
tREC
tREC
tID
tDO
tDP
tDA
tGTP
tGTA
DTMF COMPOSITE INPUT SIGNAL.
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
4-BIT DECODED DATA IN RECEIVE DATA REGISTER
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.
INDICATES THAT VALID DATA IS IN THE RECEIVE DATA REGISTER. THE BIT IS CLEARED AFTER THE STATUS
REGISTER IS READ.
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.
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION.
MINIMUM TIME BETWEEN VALID SEQUENTIAL DTMF SIGNALS.
MAXIMUM ALLOWABLE DROPOUT DURING VALID DTMF SIGNAL.
TIME TO DETECT VALID FREQUENCIES PRESENT.
TIME TO DETECT VALID FREQUENCIES ABSENT.
GUARD TIME, TONE PRESENT.
GUARD TIME, TONE ABSENT.
Figure 9 - Description of Timing Events
7.0
DTMF Generator
The DTMF transmitter employed in the MT8888C 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 Table 1 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 94 Hz. The high group
frequencies are 1209, 1336, 1477 and 1633 Hz. Typically, the high group to low group amplitude ratio (twist) is 2 dB
to compensate for high group attenuation on long loops.
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 of time
segments is fixed at 32, however, by varying the segment length as described above the frequency can also be
varied. The divider output clocks another counter, which addresses the sinewave lookup ROM.
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
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 8 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
8.0
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 ms±1 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, the burst/pause duration is doubled to 102 ms ±2 ms. 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 time is desirable, a software timing loop or external timer can be used to provide the timing pulses
when the burst mode is disabled by enabling and disabling the transmitter.
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Zarlink Semiconductor Inc.
MT8888C
9.0
Data Sheet
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.
OUTPUT FREQUENCY (Hz)
ACTIVE
INPUT
SPECIFIED
ACTUAL
L1
697
699.1
+0.30
L2
770
766.2
-0.49
L3
852
847.4
-0.54
L4
941
948.0
+0.74
H1
1209
1215.9
+0.57
H2
1336
1331.7
-0.32
H3
1477
1471.9
-0.35
H4
1633
1645.0
+0.73
%ERROR
Table 2 - Actual Frequencies Versus Standard Requirements
10.0
Distortion Calculations
The MT8888C is capable of producing precise tone bursts with minimal error in frequency (see Table 2). 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.
V22f + V23f + V24f + .... V2nf
THD (%) = 100
Vfundamental
Figure 11 - Equation 1. THD (%) For a Single Tone
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 using Equation 2. VL 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 switched-capacitor filter following the D/A converter keeps distortion products down to a very low level as
shown in Figure 10.
V22L + V23L + .... V2nL + V22H +
V23H + .. V2nH + V2IMD
THD (%) = 100
V2L + V2H
Figure 12 - Equation 2. THD (%) For a Dual Tone
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Zarlink Semiconductor Inc.
MT8888C
11.0
Data Sheet
DTMF Clock Circuit
The internal clock circuit is completed with the addition of a standard television color burst crystal. The crystal
specification is as follows:
Frequency:
3.579545 MHz
Frequency Tolerance:
±0.1%
Resonance Mode:
Parallel
Load Capacitance:
18pF
Maximum Series Resistance: 150 ohms
Maximum Drive Level:
e.g.
2mW
CTS Knights MP036S
Toyocom
TQC-203-A-9S
A number of MT8888C devices can be connected as shown in Figure 13 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.
MT8888C
MT8888C
MT8888C
OSC1 OSC2
OSC1 OSC2
OSC1 OSC2
3.579545 MHz
Figure 13 - Common Crystal Connection
12.0
Microprocessor Interface
The MT8888C incorporates an Intel microprocessor interface which is compatible with fast versions (16 MHz) of the
80C51. No wait cycles need to be inserted.
Figure 19 and Figure 20 are the timing diagrams for the Intel 8031, 8051 and 8085 (5 MHz) microcontrollers. By
NANDing the address latch enable (ALE) output with the high-byte address (P2) decode output, CS is generated.
Figure 14 summarizes the connection of these Intel processors to the MT8888C transceiver.
The microprocessor interface provides access to five internal registers. The read-only Receive Data Register
contains the decoded output of the last valid DTMF digit received. Data entered into the write-only Transmit Data
Register will determine which tone pair is to be generated (see Table 1 for coding details). Transceiver control is
accomplished with two control registers (see Table 6 and Table 7), CRA and CRB, which have the same address. A
write operation to CRB is executed by first setting the most significant bit (b3) in CRA. The following write operation
to the same address will then be directed to CRB, and subsequent write cycles will be directed back to CRA. The
read-only status register indicates the current transceiver state (see Table 8).
A software reset must be included at the beginning of all programs to initialize the control registers upon power-up
or power reset (see Figure 19). Refer to Tables 4-7 for bit descriptions of the two control registers.
The multiplexed IRQ/CP pin can be programmed to generate an interrupt upon validation of DTMF signals or when
the transmitter is ready for more data (burst mode only). Alternatively, this pin can be configured to provide a
squarewave output of the call progress signal. The IRQ/CP pin is an open drain output and requires an external
pull-up resistor (see Figure 15).
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Zarlink Semiconductor Inc.
MT8888C
Data Sheet
RS0
WR
RD
0
0
1
Write to Transmit Data Register
0
1
0
Read from Receive Data Register
1
0
1
Write to Control Register
1
1
0
Read from Status Register
Table 3 - Internal Register Functions
b3
RSEL
FUNCTION
b2
b1
b0
IRQ
CP/DTMF
TOUT
Table 4 - CRA Bit Positions
b3
b2
b1
b0
C/R
S/D
TEST
BURST
ENABLE
Table 5 - CRB Bit Positions
BIT
NAME
DESCRIPTION
b0
TOUT
Tone Output Control. A logic high enables the tone output; a logic low turns the tone output
off. This bit controls all transmit tone functions.
b1
CP/DTMF
Call Progress or DTMF Mode Select. A logic high enables the receive call progress mode;
a logic low enables DTMF mode. In DTMF mode the device is capable of receiving and
transmitting DTMF signals. In CP mode a rectangular wave representation of the received
tone signal will be present on the IRQ/CP output pin if IRQ has been enabled (control
register A, b2=1). In order to be detected, CP signals must be within the bandwidth
specified in the AC Electrical Characteristics for Call Progress.
Note: DTMF signals cannot be detected when CP mode is selected.
b2
IRQ
Interrupt Enable. A logic high enables the interrupt function; a logic low deactivates the
interrupt function. When IRQ is enabled and DTMF mode is selected (control register A,
b1=0), the IRQ/CP output pin will go low when either 1) a valid DTMF signal has been
received for a valid guard time duration, or 2) the transmitter is ready for more data (burst
mode only).
b3
RSEL
Register Select. A logic high selects control register B for the next write cycle to the control
register address. After writing to control register B, the following control register write cycle
will be directed to control register A.
Table 6 - Control Register A Description
13
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
BIT
NAME
DESCRIPTION
b0
BURST
Burst Mode Select. A logic high deactivates burst mode; a logic low enables burst mode.
When activated, the digital code representing a DTMF signal (see Table 1) can be written
to the transmit register, which will result in a transmit DTMF tone burst and pause of equal
durations (typically 51 msec). Following the pause, the status register will be updated (b1 Transmit Data Register Empty), and an interrupt will occur if the interrupt mode has been
enabled.
When CP mode (control register A, b1) is enabled the normal tone burst and pause
durations are extended from a typical duration of 51 msec to 102 msec.
When BURST is high (deactivated) the transmit tone burst duration is determined by the
TOUT bit (control register A, b0).
b1
TEST
Test Mode Control. A logic high enables the test mode; a logic low deactivates the test
mode. When TEST is enabled and DTMF mode is selected (control register A, b1=0), the
signal present on the IRQ/CP pin will be analogous to the state of the DELAYED
STEERING bit of the status register (see Figure 7, signal b3).
b2
S/D
Single or Dual Tone Generation. A logic high selects the single tone output; a logic low
selects the dual tone (DTMF) output. The single tone generation function requires further
selection of either the row or column tones (low or high group) through the C/R bit (control
register B, b3).
b3
C/R
Column or Row Tone Select. A logic high selects a column tone output; a logic low selects
a row tone output. This function is used in conjunction with the S/D bit (control register B,
b2).
Table 7 - Control Register B Description
BIT
NAME
b0
IRQ
STATUS FLAG SET
STATUS FLAG CLEARED
Interrupt has occurred. Bit one
(b1) or bit two (b2) is set.
Interrupt is inactive. Cleared after
Status Register is read.
b1
TRANSMIT DATA
REGISTER EMPTY
(BURST MODE ONLY)
Pause duration has terminated
and transmitter is ready for new
data.
Cleared after Status Register is
read or when in non-burst mode.
b2
RECEIVE DATA REGISTER
FULL
Valid data is in the Receive Data
Register.
Cleared after Status Register is
read.
b3
DELAYED STEERING
Set upon the valid detection of
the absence of a DTMF signal.
Cleared upon the detection of a
valid DTMF signal.
Table 8 - Status Register Description
14
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
8031/8051
8080/8085
MT8888C
A8-A15
CS
A8
RS0
D0-D3
PO
RD
WR
RD
WR
Figure 14 - MT8888C Interface Connections for Various Intel Micros
VDD
MT8880C
C1
R1
DTMF/CP
INPUT
R2
VDD
IN-
St/GT
GS
ESt
DTMF
OUTPUT
Notes:
R1, R2 = 100 kΩ 1%
R3 = 374 kΩ 1%
R4 = 3.3 kΩ 10%
R5 = 4.7 MΩ 10%
RL = 10 k Ω (min.)
C1 = 100 nF 5%
C2 = 100 nF 5%
C3 = 100 nF 10%*
C4 = 10 nF 10%
X-tal = 3.579545 MHz
C4
RL
C2
R4
VRef
D3
VSS
D2
OSC1
D1
OSC2
D0
TONE
IRQ/CP
R5
X-tal
C3
IN+
WR
RD
CS
RS0
R3
To µP
or µC
* Microprocessor based systems can inject undesirable noise into the supply rails.
The performance of the MT8888C 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 15 - Application Circuit (Single-Ended Input)
15
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
5.0 VDC
5.0 VDC
MMD6150 (or
equivalent)
2.4 kΩ
130 pF
3 kΩ
TEST POINT
TEST POINT
24 kΩ
100 pF
MMD7000 (or
equivalent)
Test load for IRQ/CP pin
Test load for D0-D3 pins
Figure 16 - Test Circuits
INITIALIZATION PROCEDURE
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:
1)
2)
3)
4)
5)
6)
Read Status Register
Write to Control Register
Write to Control Register
Write to Control Register
Write to Control Register
Read Status Register
RS0
1
1
1
1
1
1
Control
WR
1
0
0
0
0
1
RD
0
1
1
1
1
0
b3
X
0
0
1
0
X
TYPICAL CONTROL SEQUENCE FOR BURST MODE APPLICATIONS
Transmit DTMF tones of 50 ms burst/50 ms pause and Receive DTMF Tones.
Sequence:
RS0
WR
RD
b3
1) Write to Control Register A
1
0
1
1
(tone out, DTMF, IRQ, Select Control Register B)
2) Write to Control Register B
1
0
1
0
(burst mode)
3) Write to Transmit Data Register
0
0
1
0
(send a digit 7)
4) Wait for an interrupt or poll Status Register
5) Read the Status Register
1
1
0
X
-if bit 1 is set, the Tx is ready for the next tone, in which case...
Write to Transmit Register
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
1
Data
b2
X
0
0
0
0
X
b1
X
0
0
0
0
X
b0
X
0
0
0
0
X
b2
1
b1
0
b0
1
0
0
0
1
1
1
X
X
X
1
0
1
0
1
0
X
X
X
X
-if both bits are set...
Read the Receive Data Register
0
1
0
X
X
X
X
Write to Transmit Data Register
0
0
1
0
1
0
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 17 - Application Notes
16
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
Absolute Maximum Ratings*
Parameter
Symbol
1
Power supply voltage VDD-VSS
2
Voltage on any pin
3
Current at any pin (Except VDD and VSS)
4
Storage temperature
TST
5
Package power dissipation
PD
Min.
Max.
6
V
VSS-0.3
VDD+0.3
V
10
mA
+150
°C
1000
mW
VDD
VI
-65
Units
* 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
Sym.
Min.
Typ.‡
Max.
Units
5.00
5.25
V
+85
°C
3.583124
MHz
1
Positive power supply
VDD
4.75
2
Operating temperature
TO
-40
3
Crystal clock frequency
fCLK
3.575965
3.579545
Test Conditions
‡ 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.
Sym.
Min.
Typ.‡
Max.
Units
Operating supply voltage
VDD
4.75
5.0
5.25
V
Operating supply current
IDD
7.0
11
mA
Power consumption
PC
57.8
mW
Characteristics
1
2
3
4
5
6
S
U
P
I
N
P
U
T
S
7
8
9
10
O
U
T
P
U
T
S
11
12
13
14
15
16
D
i
g
i
t
a
l
Data
Bus
High level input voltage
(OSC1)
VIHO
Low level input voltage
(OSC1)
VILO
Steering threshold voltage
VTSt
Low level output voltage
(OSC2)
VOLO
High level output voltage
(OSC2)
VOHO
3.5
2.2
2.3
V
Note 9*
1.5
V
Note 9*
2.5
V
VDD=5V
0.1
V
No load
Note 9*
V
No load
Note 9*
4.9
Output leakage current
(IRQ)
IOZ
VRef output voltage
VRef
VRef output resistance
ROR
Low level input voltage
VIL
High level input voltage
VIH
Input leakage current
IIZ
Source current
IOH
-1.4
Sink current
IOL
2.0
2.4
Test Conditions
1
10
µA
VOH=2.4 V
2.5
2.6
V
No load, VDD=5V
1.3
kΩ
0.8
2.0
V
V
µA
VIN=VSS to VDD
-6.6
mA
VOH=2.4V
4.0
mA
VOL=0.4V
10
17
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
DC Electrical Characteristics (continued) - † - VSS=0 V. (continued)
Characteristics
17
18
19
ESt
and
St/Gt
IRQ/
CP
Sym.
Min.
Typ.‡
Max.
Units
Test Conditions
Source current
IOH
-0.5
-3.0
mA
VOH=4.6V
Sink current
IOL
2
4
mA
VOL=0.4V
Sink current
IOL
4
16
mA
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.
* See “Notes” following AC Electrical Characteristics Tables.
Electrical Characteristics Gain Setting Amplifier - Voltages are with respect to ground (VSS) unless otherwise stated,
VSS= 0V.
Characteristics
Sym.
Min.
Typ.
Max.
Units
Test Conditions
100
nA
VSS ≤ VIN ≤ VDD
1
Input leakage current
IIN
2
Input resistance
RIN
3
Input offset voltage
VOS
4
Power supply rejection
PSRR
50
dB
5
Common mode rejection
CMRR
40
dB
6
DC open loop voltage gain
AVOL
40
dB
CL = 20p
7
Unity gain bandwidth
BW
1.0
MHz
CL = 20p
8
Output voltage swing
VO
0.5
VDD-0.5
V
RL ≥ 100 kΩ to VSS
9
Allowable capacitive load (GS)
CL
100
pF
PM>40°
10
Allowable resistive load (GS)
RL
50
kΩ
VO = 4Vpp
11
Common mode range
VCM
1.0
V
RL = 50kΩ
10
MΩ
25
mV
VDD-1.0
1 kHz
Figures are for design aid only: not guaranteed and not subject to production testing.
Characteristics are over recommended operating conditions unless otherwise stated.
MT8888C AC Electrical Characteristics †
Characteristics
1
R
X
Valid input signal levels
(each tone of composite
signal)
- Voltages are with respect to ground (VSS) unless otherwise stated.
Sym.
Min.
Typ.‡
Max.
Units
Notes*
-29
+1
dBm
1,2,3,5,6
27.5
869
mVRMS
1,2,3,5,6
† Characteristics are over recommended operating conditions (unless otherwise stated) using the test circuit shown in Figure 15.
18
Zarlink Semiconductor Inc.
MT8888C
Data Sheet
AC Electrical Characteristics † - Voltages are with respect to ground (VSS) unless otherwise stated. fC=3.579545 MHz
Characteristics
Sym.
Typ.‡
Min.
Max.
Units
Notes*
1
Positive twist accept
8
dB
2,3,6,9
2
Negative twist accept
8
dB
2,3,6,9
3
4
R
X
Freq. deviation accept
±1.5%± 2Hz
2,3,5
Freq. deviation reject
±3.5%
2,3,5
5
Third tone tolerance
-16
dB
2,3,4,5,9,10
6
Noise tolerance
-12
dB
2,3,4,5,7,9,10
7
Dial tone tolerance
22
dB
2,3,4,5,8,9
† Characteristics are over recommended operating conditions unless otherwise stated.
‡ Typical figures are at 25°C, VDD = 5 V, and for design aid only: not guaranteed and not subject to production testing.
* *See “Notes” following AC Electrical Characteristics Tables.
AC Electrical Characteristics†- Call Progress - Voltages are with respect to ground (VSS), unless otherwise stated.
Characteristics
Sym.
Min.
310
Typ.‡
Max.
Units
Conditions
500
Hz
@ -25 dBm,
Note 9
1
Accept Bandwidth
fA
2
Lower freq. (REJECT)
fLR
290
Hz
@ -25 dBm
3
Upper freq. (REJECT)
fHR
540
Hz
@ -25 dBm
4
Call progress tone detect level (total
power)
-30
dBm
† Characteristics are over recommended operating conditions unless otherwise stated
‡ Typical figures are at 25°C, VDD=5 V, and for design aid only: not guaranteed and not subject to production testing
AC Electrical Characteristics †- DTMF Reception - Typical DTMF tone accept and reject requirements. Actual values are
user selectable as per Figures 5, 6 and 7.
Characteristics
Sym.
Min.
Typ.‡
Max.
Units
1
Minimum tone accept duration
tREC
40
ms
2
Maximum tone reject duration
tREC
20
ms
3
Minimum interdigit pause duration
tID
40
ms
4
Maximum tone drop-out duration
tDO
20
ms
† Characteristics are over recommended operating conditions unless otherwise stated
‡ Typical figures are at 25°C, VDD=5 V, and for design aid only: not guaranteed and not subject to production testing
19
Zarlink Semiconductor Inc.
Conditions
MT8888C
Data Sheet
AC Electrical Characteristics† - Voltages are with respect to ground (VSS), unless otherwise stated.
Characteristics
1
Sym.
Min.
Typ.‡
Max.
Units
Conditions
T
O
N
E
Tone present detect time
tDP
3
11
14
ms
Note 11
Tone absent detect time
tDA
0.5
4
8.5
ms
Note 11
Delay St to b3
tPStb3
13
µs
See Figure 7
I
N
Delay St to RX0-RX3
tPStRX
8
µs
See Figure 7
5
Tone burst duration
tBST
50
52
ms
DTMF mode
6
Tone pause duration
tPS
50
52
ms
DTMF mode
7
Tone burst duration (extended)
tBSTE
100
104
ms
Call Progress mode
Tone pause duration (extended)
tPSE
100
104
ms
Call Progress mode
High group output level
VHOUT
-6.1
-2.1
dBm
RL=10kΩ
Low group output level
VLOUT
-8.1
-4.1
dBm
RL=10kΩ
Pre-emphasis
dBP
0
3
dB
RL=10kΩ
Output distortion (Single Tone)
THD
dB
25 kHz Bandwidth
2
3
4
8
9
10
11
12
T
O
N
E
O
U
T
2
-35
13
RL=10kΩ
14
Frequency deviation
15
Output load resistance
RLT
Crystal/clock frequency
fC
16
17
18
19
X
T
A
L
Clock input rise and fall time
tCLRF
Clock input duty cycle
DCCL
Capacitive load (OSC2)
±0.7
fD
10
±1.5
%
50
kΩ
3.5759 3.5795 3.5831
40
50
CLO
fC=3.579545 MHz
MHz
110
ns
Ext. clock
60
%
Ext. clock
30
pF
† Timing is over recommended temperature & power supply voltages.
‡ Typical figures are at 25°C and for design aid only: not guaranteed and not subject to production testing.
AC Electrical Characteristics†- MPU Interface - Voltages are with respect to ground (VSS), unless otherwise stated.
Characteristics
Sym.
Min.
Typ.‡
Max.
Units
Conditions
1
RD/WR clock frequency
fCYC
4.0
MHz
Figure 18
2
RD/WR cycle period
tCYC
250
ns
Figure 18
3
RD/WR rise and fall time
tR, tF
ns
Figure 18
4
Address setup time
tAS
23
ns
Figures 19 & 20
5
Address hold time
tAH
26
ns
Figures 19 & 20
6
Data hold time (read)
tDHR
22
ns
Figures 19 & 20
7
RD to valid data delay (read)
tDDR
ns
Figures 19 & 20
8
RD, WR pulse width low
tPWL
ns
Figures 18, 19 & 20
9
RD, WR pulse width high
tPWH
ns
Figures 18, 19 & 20
10
Data setup time (write)
tDSW
45
ns
Figures 19 & 20
11
Data hold time (write)
tDHW
10
ns
Figures 19 & 20
12
Input Capacitance (data bus)
20
100
150
100
5
CIN
20
Zarlink Semiconductor Inc.
pF
MT8888C
Data Sheet
AC Electrical Characteristics†- MPU Interface (continued)- Voltages are with respect to ground (VSS), unless otherwise
Characteristics
Sym.
Min.
Typ.‡
Max.
Units
COUT
5
pF
13 Output Capacitance (IRQ/CP)
† Characteristics are over recommended operating conditions unless otherwise stated
‡ Typical figures are at 25°C, VDD=5 V, and for design aid only: not guaranteed and not subject to production testing
Notes:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
dBm=decibels above or below a reference power of 1 mW into a 600 ohm load.
Digit sequence consists of all 16 DTMF tones.
Tone duration=40 ms. Tone pause=40 ms.
Nominal DTMF frequencies are used.
Both tones in the composite signal have an equal amplitude.
The tone pair is deviated by ± 1.5%±2 Hz.
Bandwidth limited (3 kHz) Gaussian noise.
The precise dial tone frequencies are 350 and 440 Hz (±2%).
Guaranteed by design and characterization. Not subject to production testing.
Referenced to the lowest amplitude tone in the DTMF signal.
For guard time calculation purposes.
tCYC
tR
tF
tPWH
RD/WR
tPWL
Figure 18 - RD/WR Clock Pulse
tPWL
RD
tPWH
tAS
tAH
CS, RS0
tDHR
tDDR
DATA BUS
Figure 19 - 8031/8051/8085 Read Timing Diagram
tPWL
WR
tPWH
tAS
tAH
CS, RS0
tDSW
tDHW
DATA BUS
Figure 20 - 8031/8051/8085 Write Timing Diagram
21
Zarlink Semiconductor Inc.
Conditions
For more information about all Zarlink products
visit our Web Site at
www.zarlink.com
Information relating to products and services furnished herein by Zarlink Semiconductor Inc. or its subsidiaries (collectively “Zarlink”) is believed to be reliable.
However, Zarlink assumes no liability for errors that may appear in this publication, or for liability otherwise arising from the application or use of any such
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of any order or contract nor to be regarded as a representation relating to the products or services concerned. The products, their specifications, services and other
information appearing in this publication are subject to change by Zarlink without notice. No warranty or guarantee express or implied is made regarding the
capability, performance or suitability of any product or service. Information concerning possible methods of use is provided as a guide only and does not constitute
any guarantee that such methods of use will be satisfactory in a specific piece of equipment. It is the user’s responsibility to fully determine the performance and
suitability of any equipment using such information and to ensure that any publication or data used is up to date and has not been superseded. Manufacturing does
not necessarily include testing of all functions or parameters. These products are not suitable for use in any medical products whose failure to perform may result in
significant injury or death to the user. All products and materials are sold and services provided subject to Zarlink’s conditions of sale which are available on request.
Purchase of Zarlink’s I2C components conveys a licence under the Philips I2C Patent rights to use these components in and I2C System, provided that the system
conforms to the I2C Standard Specification as defined by Philips.
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