Mitel MT8888CS Integrated dtmftransceiver with intel micro interface Datasheet

MT8888C/MT8888C-1

Integrated DTMF Transceiver
with Intel Micro Interface
Features
ISSUE 2
•
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 -30dBm
Ordering
MT8888CE/CE-1
MT8888CC/CC-1
MT8888CS/CS-1
MT8888CN/CN-1
•
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 utilizes an Intel micro interface, which
allows the device to be connected to a number of
popular microcontrollers with minimal external logic.
The MT8888C-1 is functionally identical to the
MT8888C except the receiver is enhanced to accept
lower level signals, and also has a specified low
signal rejection level.
Description
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-
-
Row and
Column
Counters
D/A
Converters
∑
Dial
Tone
Filter
High Group
Filter
OSC2
Low Group
Filter
Oscillator
Circuit
Control
Logic
Bias
Circuit
V DD VRef
VSS
Transmit Data
Register
Status
Register
Control
Logic
GS
OSC1
Information
20 Pin Plastic DIP
20 Pin Ceramic DIP
20 Pin SOIC
24 Pin SSOP
-40°C to +85°C
Applications
TONE
May 1995
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
Receive Data
Register
RD
I/O
Control
CS
R/W
RS0
St/GT
Figure 1 - Functional Block Diagram
4-91
MT8888C/MT8888C-1
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
RD
RS0
IN+
INGS
VRef
VSS
OSC1
OSC2
NC
NC
TONE
R/W
CS
20 PIN CERDIP/PLASTIC DIP/SOIC
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
RD
RS0
24 PIN SSOP
Figure 2 - Pin Connections
Pin Description
Pin #
Name
Description
20
24
1
1
IN+
Non-inverting op-amp input.
2
2
IN-
Inverting op-amp input.
3
3
GS
Gain Select. Gives access to output of front end differential amplifier for connection of
feedback resistor.
4
4
VRef
Reference Voltage output (VDD/2).
5
5
VSS
Ground (0V).
6
6
OSC1 Oscillator input. This pin can also be driven directly by an external clock.
7
7
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
TONE Output from internal DTMF transmitter.
9
11
WR
Write microprocessor input. TTL compatible.
10
12
CS
Chip Select input. Active Low. This signal must be qualified externally by address latch
enable (ALE) signal, see Figure 12.
11
13
RS0
Register Select input. Refer to Table 3 for bit interpretation. TTL compatible.
12
14
RD
Read microprocessor input. TTL compatible.
13
15
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.
1417
1821
18
22
19
23
20
24
VDD
Positive power supply (5V typ.).
8,9
16,17
NC
No Connection.
4-92
D0-D3 Microprocessor Data Bus. High impedance when CS = 1 or RD = 1.
TTL compatible.
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.
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.
MT8888C/MT8888C-1
Functional Description
The
MT8888C/MT8888C-1
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/MT8888C-1 internal registers.
C1
R1
IN+
INC2
R4
R5
GS
R2
R3
VRef
Input Configuration
MT8888C/
MT8888C-1
The input arrangement of the MT8888C/MT8888C-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
gain adjustment. In a single-ended configuration, the
input pins are connected as shown in Figure 3.
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
Figure 4 shows the necessary connections for a
differential input configuration.
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.
IN+
IN-
RIN
RF
GS
VRef
VOLTAGE GAIN
(AV) = RF / RIN
R12 + (1/ωC)2
Figure 4 - Differential Input Configuration
Receiver Section
C
(ZINdiff) = 2
MT8888C/
MT8888C-1
Figure 3 - Single-Ended Input Configuration
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
0= LOGIC LOW, 1= LOGIC HIGH
Table 1. Functional Encode/Decode Table
4-93
MT8888C/MT8888C-1
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.
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 (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 Table 1)
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
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 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/
MT8888C-1
C1
VDD
Vc
St/GT
ESt
R1
tGTA = (R1C1) In (VDD / VTSt)
tGTP = (R1C1) In [VDD / (VDD-VTSt)]
Figure 5 - Basic Steering Circuit
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 ≥ t DPmax+tGTPmax - tDAmin
tREC ≤ tDPmin+tGTPmin - tDAmax
tID ≥ tDAmax+tGTAmax - tDPmin
tDO ≤ tDAmin+tGTAmin - tDPmax
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 µF is recommended for most
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
4-94
MT8888C/MT8888C-1
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 t DO 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.
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.
LEVEL
(dBm)
Call Progress Filter
0
A call progress mode, using the MT8888C/
MT8888C-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
EVENTS
AAAAAAAAA
AAAA
AAAA
AAAAAA
AAAAAAAA
AAAA
AAAAAAAA
AAAA
AAAA
AAAAAAAAAAAAAA
-25
A
Figure 8 - Call Progress Response
C
D
E
F
tDO
tID
TONE
#n + 1
TONE #n
TONE
#n + 1
tDA
tDP
ESt
750
= May Accept
AAAAAAAA
AAAAAA
AAAA
AA
= Accept
AAAA
AAAAAAAA
AAAAAA
AA
tREC
Vin
500
FREQUENCY (Hz)
= Reject
B
tREC
250
tGTP
tGTA
VTSt
St/GT
tPStRX
RX0-RX3
DECODED TONE # (n-1)
#n
# (n + 1)
tPStb3
b3
b2
Read
Status
Register
IRQ/CP
Figure 7 - Receiver Timing Diagram
4-95
MT8888C/MT8888C-1
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.
INTERRUPT IS ACTIVE INDICATING THAT NEW DATA IS IN THE RX DATA REGISTER. THE INTERRUPT IS
IRQ/CP
CLEARED AFTER THE STATUS REGISTER IS READ.
tREC
MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID.
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 9 - Description of Timing Events
DTMF Generator
The DTMF transmitter employed in the MT8888C/
MT8888C-1 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 941 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
4-96
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.
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.
MT8888C/MT8888C-1
Scaling Information
10 dB/Div
Start Frequency = 0 Hz
Stop Frequency = 3400 Hz
Marker Frequency = 697 Hz and
1209 Hz
Figure 10 - Spectrum Plot
Burst Mode
ACTIVE
INPUT
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.
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)
%ERROR
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
Table 2. Actual Frequencies Versus Standard
Requirements
Distortion Calculations
The MT8888C/MT8888C-1 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
Equation 1. THD (%) For a Single Tone
4-97
MT8888C/MT8888C-1
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. 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
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
Equation 2. THD (%) For a Dual Tone
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:
3.579545 MHz
±0.1%
Frequency Tolerance:
Resonance Mode:
Parallel
Load Capacitance:
18pF
Maximum Series Resistance:150 ohms
Maximum Drive Level:
2mW
e.g.
CTS Knights MP036S
Toyocom TQC-203-A-9S
A number of MT8888C/MT8888C-1 devices can be
connected as shown in Figure 11 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-1
OSC1 OSC2
MT8888C/
MT8888C-1
OSC1 OSC2
MT8888C/
MT8888C-1
OSC1 OSC2
Figures 17 and 18 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 12 summarizes the connection of
these Intel processors to the MT8888C/MT8888C-1
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 Tables 6 and 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 17). 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 13).
RS0
WR
RD
FUNCTION
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
3.579545 MHz
Figure 11 - Common Crystal Connection
b3
b2
b1
b0
RSEL
IRQ
CP/DTMF
TOUT
Table 4. CRA Bit Positions
Microprocessor Interface
The MT8888C/MT8888C-1 incorporates an Intel
microprocessor interface which is compatible with
fast versions (16 MHz) of the 80C51. No wait cycles
need to be inserted.
4-98
b3
b2
b1
b0
C/R
S/D
TEST
BURST
ENABLE
Table 5. CRB Bit Positions
MT8888C/MT8888C-1
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 de-activates 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
BIT
NAME
DESCRIPTION
b0
BURST
Burst Mode Select. A logic high de-activates 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 (de-activated) 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 de-activates 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
4-99
MT8888C/MT8888C-1
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
8031/8051
8080/8085
MT8888C/MT8888C-1
A8-A15
CS
A8
RS0
D0-D3
PO
RD
WR
RD
WR
Figure 12 - MT8888C Interface Connections for Various Intel Micros
VDD
MT8888C/MT8888C-1
C1
DTMF/CP
INPUT
R1
R2
IN+
VDD
IN-
St/GT
GS
ESt
DTMF
OUTPUT
RL
Notes:
R1, R2 = 100 kΩ 1%
R3 = 374 Ω 1%
R4 = 3.3 kΩ 10%
RL = 10 k Ω (min.)
C1 = 100 nF 5%
C2 = 100 nF 5%
C3 = 100 nF 10%*
X-tal = 3.579545 MHz
C2
R4
VRef
D3
VSS
D2
OSC1
D1
OSC2
D0
TONE
IRQ/CP
X-tal
C3
WR
RD
CS
RS0
R3
* Microprocessor based systems can inject undesirable noise into the supply rails.
The performance of the MT8888C/MT8888C-1 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)
4-100
To µP
or µC
MT8888C/MT8888C-1
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 D0-D3 pins
Test load for IRQ/CP pin
Figure 14 - Test Circuits
INITIALIZATION PROCEDURE
A software reset must be included at the beginning of all programs to initialize the control registers
power up.The initialization procedure should be implemented 100ms after power up.
Description:
Control
Data
RD
b3
b2
b1
RS0
WR
1) Read Status Register
1
1
0
X
X
X
2) Write to Control Register
1
0
1
0
0
0
3) Write to Control Register
1
0
1
0
0
0
4) Write to Control Register
1
0
1
1
0
0
5) Write to Control Register
1
0
1
0
0
0
6) Read Status Register
1
1
0
X
X
X
after
b0
X
0
0
0
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
1
B)
1
WR
0
RD
1
b3
1
b2
1
b1
0
b0
1
0
1
0
0
0
0
0
0
1
0
1
1
1
1
1
0
X
X
X
X
1
0
1
0
1
-if bit 2 is set, a DTMF tone has been received, in which case....
Read the Receive Data Register
0
1
0
X
X
X
X
-if both bits are set...
Read the Receive Data Register
Write to Transmit Data Register
0
1
X
0
X
1
X
0
X
1
1) Write to Control Register A
(tone out, DTMF, IRQ, Select Control Register
2) Write to Control Register B
(burst mode)
3) Write to Transmit Data Register
(send a digit 7)
4) Wait for an interrupt or poll Status Register
5) Read the Status Register
-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)
0
0
1
0
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 15 - Application Notes
4-101
MT8888C/MT8888C-1
Absolute Maximum Ratings*
Parameter
1
2
3
Symbol
Power supply voltage VDD-VSS
Voltage on any pin
Min
Max
Units
6
V
VDD+0.3
V
10
mA
+150
°C
1000
mW
VDD
VI
VSS-0.3
4
Current at any pin (Except VDD and VSS)
Storage temperature
TST
5
Package power dissipation
PD
-65
* 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
1
Positive power supply
VDD
4.75
2
Operating temperature
TO
-40
Test Conditions
3.575965 3.579545 3.583124
MHz
3 Crystal clock frequency
fCLK
‡ 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
13
14
15
16
17
18
19
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
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
ESt
and
St/Gt
Source current
IRQ/
CP
D
i
g
i
t
a
l
Data
Bus
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)
11
12
High level input voltage
(OSC1)
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
10
µA
VIN=VSS to VDD
-6.6
mA
VOH=2.4V
2.0
4.0
mA
VOL=0.4V
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.
4-102
MT8888C/MT8888C-1
Electrical Characteristics
Gain Setting Amplifier - Voltages are with respect to ground (VSS) unless otherwise stated, VSS= 0V, VDD=5V, TO=25°C.
Characteristics
Sym
Typ‡
Min
Max
Units
Test Conditions
VSS ≤ VIN ≤ VDD
1
Input leakage current
IIN
±100
nA
2
Input resistance
RIN
10
MΩ
3
Input offset voltage
VOS
25
mV
4
Power supply rejection
PSRR
60
dB
1 kHz
5
Common mode rejection
CMRR
60
dB
0.75 ≤ VIN ≤ 4.25V
6
DC open loop voltage gain
AVOL
65
dB
7
Unity gain bandwidth
BW
1.5
MHz
8
Output voltage swing
VO
4.5
Vpp
9
Allowable capacitive load (GS)
CL
100
pF
10
Allowable resistive load (GS)
RL
50
kΩ
11
Common mode range
VCM
3.0
Vpp
RL ≥ 100 kΩ to VSS
No Load
‡ Typical figures are at 25°C and for design aid only: not guaranteed and not subject to production testing.
MT8888C-1 AC Electrical Characteristics† - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics
1
2
R
X
Sym
Valid input signal levels
(each tone of composite
signal)
Input Signal Level Reject
Min
Typ
Max
Units
-31
+1
dBm
1,2,3,5,6
21.8
869
mVRMS
1,2,3,5,6
dBm
1,2,3,5,6
-37
10.9
mVRMS
† Characteristics are over recommended temperature and at VDD=5V, using the test circuit shown in Figure 13.
Notes*
1,2,3,5,6
MT8888C AC Electrical Characteristics† - Voltages are with respect to ground (VSS) unless otherwise stated.
Characteristics
1
R
X
Sym
Valid input signal levels
(each tone of composite
signal)
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 13.
AC Electrical Characteristics† - Voltages are with respect to ground (VSS) unless otherwise stated. fC=3.579545 MHz
Characteristics
Sym
Min
Typ‡
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 = 5V, and for design aid only: not guaranteed and not subject to production testing.
* *See “Notes” following AC Electrical Characteristics Tables.
4-103
MT8888C/MT8888C-1
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=5V, 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
Conditions
4 Maximum tone drop-out duration
tOD
20
ms
† 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
AC Electrical Characteristics† - Voltages are with respect to ground (VSS), unless otherwise stated.
Sym
Min
Typ‡
Max
Units
Tone present detect time
tDP
3
11
14
ms
Note 11
Tone absent detect time
tDA
0.5
4
8.5
ms
Note 11
Characteristics
1
2
3
4
T
O
N
E
I
N
Conditions
Delay St to b3
tPStb3
13
µs
See Figure 7
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
8
9
10
11
12
T
O
N
E
O
U
T
2
-35
RL=10kΩ
13
±0.7
14
Frequency deviation
15
Output load resistance
RLT
10
Crystal/clock frequency
fC
3.5759
16
17
18
X
T
A
L
fD
Clock input rise and fall time
tCLRF
Clock input duty cycle
DCCL
40
3.5795
50
±1.5
%
50
kΩ
3.5831
MHz
110
ns
Ext. clock
60
%
Ext. clock
30
pF
19
Capacitive load (OSC2)
CLO
† 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.
4-104
fC=3.579545 MHz
MT8888C/MT8888C-1
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 16
2
RD/WR cycle period
tCYC
250
ns
Figure 16
3
RD/WR rise and fall time
tR, tF
ns
Figure 16
4
Address setup time
tAS
23
ns
Figures 17 & 18
5
Address hold time
tAH
26
ns
Figures 17 & 18
6
Data hold time (read)
tDHR
22
ns
Figures 17 & 18
7
RD to valid data delay (read)
tDDR
ns
Figures 17 & 18
8
RD, WR pulse width low
tPWL
ns
Figures 16, 17 & 18
9
RD, WR pulse width high
tPWH
ns
Figures 16, 17 & 18
10
Data setup time (write)
tDSW
45
ns
Figures 17 & 18
11
Data hold time (write)
tDHW
10
ns
Figures 17 & 18
12
Input Capacitance (data bus)
CIN
5
pF
13
Output Capacitance (IRQ/CP)
C OUT
5
pF
20
100
150
100
† 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
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) Guaranteed by design and characterization. Not subject to production testing.
10) Referenced to the lowest amplitude tone in the DTMF signal.
11) For guard time calculation purposes.
4-105
MT8888C/MT8888C-1
tCYC
tR
tF
tPWH
RD/WR
tPWL
Figure 16 - RD/WR Clock Pulse
tPWL
RD
tPWH
tAS
tAH
CS, RS0
tDHR
tDDR
DATA BUS
Figure 17 - 8031/8051/8085 Read Timing Diagram
tPWL
RD
tPWH
tAS
tAH
CS, RS0
tDSW
tDHW
DATA BUS
Figure 18 - 8031/8051/8085 Write Timing Diagram
4-106