CM8888 Datasheet, PDF (6/13 Pages) California Micro Devices Corp – CMOS INTEGRATED DTMF TRANCEIVER

CALIFORNIA MICRO DEVICES
CM8888/8888-2
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.
Acceptance dropout of tone #n + 1, tone
absent duration invalid, data remains
unchanged.
F.
End of tone #n + 1 detected, tone absent
duration valid, inforamtion in RX data register
retained until next valid tone repair.
Explanation Symbols
V_IN
DTMF composite input signal.
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
freqeuncies have been present/absent for
the required guard time thus consituting a
valid siganal.
b2
Indicates that valid data is in the receive
data register. The bit is cleared after the
status register is read.
IRQ/CP Interupt is active indicating that new data
is in the RX data register. The interupt is
cleared after the status register is read.
tREC Maximum DTMF signal duration not
detected as valid.
tREC Minimum DTMF signal duration required
for valid recognition.
t_ID
Minimum time between valid sequencial
DTMF signals.
t_DO
Maximum allowable dropout during valid
DTMF signal.
t_DP
Time to detect valid frequencies present.
t_DA
Time to detect valid frequencies absent.
t_GTP
Guard time, tone present.
t_GTA
Guard time, tone absent.
Functional Description
The CM8888 Integrated DTMF Transceiver provides the design
engineer with not only low power consumption, but central
office quality performance. The CM8888’s internal architecture
consists of high performance DTMF receiver with an internal
Gain Setting Amplifier and DTMF gernerator. The DTMF
Generator contains a Tone Burst Counter for generating precise
tone bursts and pauses. The Call Progress mode, when
selected, allows the detection of call progress tones. A
standard 8051, 8086/8 series microprocessor interface allows
access to an internal status register, two control registers and
two data registers within the CM8888.
Input Configuration
The CM8888 input arrangement consists of a differential input
operational amplifier and bias sources (V_REF) for biasing the
amplifier inputs at V_DD/2. Provisions are made for the
connection of a feedback resistor to the op amp output (GS) for
gain adjustment. In the single-ended configuration, the input
pins should be connected as shown in Figure 1, while Figure 2
shows the necessary connections for a differential input
configuration.
©2000 California Micro Devices Corp. All rights reserved.
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