RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
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Table 2-3. MDP Hardware Interface Signal Definitions (Cont'd)
Label
I/O Type
Signal Name/Description
TELEPHONE LINE INTERFACE
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. The output characteristics are the same as a 1458 type op amp.
RIN
I(DA)
Receive Analog. RIN is a single-ended receive data input from the telephone line interface or an optional
external hybrid circuit. The input impedance is > 70k ohms.
~OH
OD
Off-Hook Relay Control. The ~OH output can directly drive a +5V reed relay coil with a minimum resistance of
360 ohms and having a must-operate voltage of 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). ~OH is controlled by the RA bit in interface memory.
In a typical application, ~OH is connected to the normally open Off-Hook relay. In this case, ~OH active closes
the relay to connect the modem to the telephone line.
~TALK
OD
Talk/Data Relay Control. The ~TALK output can directly drive a +5V reed relay coil with a minimum resistance
of 360 ohms and having a must-operate voltage of 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). ~TALK is controlled by the RB bit in interface memory.
In a typical application, ~TALK is connected to the normally closed Talk/Data relay. In this case, ~TALK active
opens the relay to disconnect the handset from the telephone line.
SPEAKER INTERFACE
SPKR
O(DF)
Received Analog Output. The SPKR output reflects the received analog input signal. The SPKR on/off and
three levels of attenuation are controlled by bits in DSP RAM. When the speaker is turned off, the SPKR output
is clamped to the voltage at the VC pin. The SPKR output can drive an impedance as low as 300 ohms. In a
typical application, the SPKR output is an input to an external audio power amplifier.
GENERAL PURPOSE INPUT/OUTPUT LINES
GPI0-GPI7
IA
General Purpose Inputs. Eight general purpose input (GPI) pins are available to the host for programming via
the modem interface memory.
RINGD (GPI7)
IA
Ring Frequency Detected. The RINGD signal from the DAA, when connected to the GPI7 input, is monitored
for pulses in the range of 15 Hz to 68 Hz (with an 8000 Hz sample rate). The frequency detection range may be
changed by the host in DSP RAM. The circuit driving RINGD should be a 4N35 optoisolator or equivalent. The
circuit driving RINGD should not respond to momentary bursts of ringing less than 125 ms in duration, or less
than 40 VRMS (15 Hz to 68 Hz) across TIP and RING. The RI status bit in the interface memory reflects the
logic level on the GPI7 pin.
GPO0-GPO7
OB
General Purpose Outputs. Eight general purpose output (GPO) pins are available to the host for programming
via the modem interface memory.
GPO0 is used by the modem to control power down mode for the IIA and XIA (unless disabled by the host).
Connect the GPO0 output to the ~SLEEP input.
GPO0-GPO7 are all set to a 1 state by a POR (power-on reset).
SPEAK (GPO5)
OB
Speaker Line Select. The SPEAK output is used to enable (SPEAK high) or disable (SPEAK low) the SPKR
output from the MDP IIA to the speaker amplifier circuit in the analog switch.
Summary of Contents for RFX144V24-S23
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