RC56D, RC336D, and RC144D Modem Device Sets Designer’s Guide
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Table 3-6. MDP Pin Signal Definitions (Cont'd)
Label
I/O Type
Signal Name/Description
TELEPHONE LINE/TELEPHONE/AUDIO INTERFACE SIGNALS AND REFERENCE VOLTAGE
TXA1, TXA2
O(DF)
Transmit Analog 1 and 2. The TXA1 and TXA2 outputs are differential outputs 180 degrees out of
phase with each other. Each output can drive a 300
Ω
load. Typically, TXA1 and TXA2 are connected to
the telephone line interface or an optional external hybrid circuit.
RIN
I(DA)
Receive Analog. RIN is a single-ended input from the telephone line interface or an optional external
hybrid circuit with 70K
Ω
input impedance. Typically, RIN is connected to telephone line interface or an
optional external hybrid circuit. NOTE: If not used, do not tie directly to ground; this input has a bias
voltage of +2.5V (VAA = +5V).
TELOUT/NC*
O(DF)
Telephone Analog Output. TELOUT is a single-ended output that can drive a 300
Ω
load. Typically,
TELOUT is connected to a telephone handset speaker circuit.
TELIN/NC*
I(DA)
Telephone Analog Input. TELIN is a single-ended input with 70K
Ω
input impedance. Typically, TELIN
is connected to a telephone handset microphone circuit. NOTE: If not used, do not tie directly to
ground; this input has a bias voltage of +2.5V (VAA = +5V).
~RLYA
OD
Relay A Control. The ~RLYA open collector output can directly drive a +5V reed relay coil with a
minimum resistance of 360 ohms (13.9 mA max. @ 5.0V) and a must-operate voltage no greater than
4.0 VDC. A clamp diode, such as a 1N4148, should be installed across the relay coil. An external
transistor can be used to drive heavier loads (e.g., electro-mechanical relays). ~RLYA is controlled by
host setting/resetting of the RA bit.
MICM
I(DA)
Modem Microphone Input. MICM is a single-ended microphone input. The input impedance is > 70k
Ω
.
NOTE: If not used, do not tie directly to ground; this input has a bias voltage of +2.5V (VAA =
+5V).
MICV/NC*
I(DA)
Voice Microphone Input. MICV is a single-ended microphone input. Typically, MICV is connected to a
microphone output for recording voice e.g., in a speakerphone application. NOTE: If not used, do not
tie directly to ground; this input has a bias voltage of +2.5V (VAA = +5V).
VREF
REF
High Voltage Reference. Connect to VC through 10 µF (polarized, + terminal to VREF) and 0.1 µF
(ceramic) in parallel.
VC
REF
Low Voltage Reference. Connect to a ferrite bead and connect the other end of the ferrite bead to
DGND through 10 µF (polarized, + terminal to VC) and 0.1 µF (ceramic) in parallel.
SPK
O(DF)
Speaker Analog Output. The SPK analog output can originate from one of five different sources: RIN,
TELIN, MICM or MICV or from the MDP’s internal voice playback mode. The SPK on/off and three levels
of attenuation are controlled by bits in DSP RAM. When the speaker is turned off, the SPK output is
clamped to the voltage at the VC pin. The SPK output can drive an impedance as low as 300 ohms. In a
typical application, the SPK output is an input to an external LM386 audio power amplifier.
SPKMD
OA
Modem Speaker Digital Output. The SPKMD digital output reflects the received analog input signal
digitized to TTL high or low level by an internal comparator to create a PC Card (PCMCIA)-compatible
signal.
~RI
OA
Ring Indicate. Not used. Leave open.
RINGD
IA
Ring Detect. Not used. Connect to MCU: VD3.3.
Содержание RC144D
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