49013-1297 <90-00034>
P
AGE
3
Input
Input (RX) to the subassembly appears at pins 2 and 4 on
connector P5.
The incoming signal passes the RX transformer (600/600 ohm), a
selectable pad (0 or -20 dB) is buffered by and then applied
through an integrated circuit to the RXD, CTS (Clear To Send),
and DCD (Data Carrier Detect) outputs.
The LED CD on the front panel lights to indicate that there is
carrier detection.
Monitor the input signal at the front panel through the line side
RCV test points.
Output
Output (TX) from the subassembly is at pins 3 and 5 on connec-
tor P5.
The data output signal is introduced at DTR (Data Terminal
Ready), RTS (Request To Send), and TXD.
The signal is routed through an integrated circuit to feed a
buffer that passes the signal to a selectable pad (0 or -20 dB) and
the coupling transformer.
To adjust the output signal level from -1 to -40 dBm, use the
potentiometer, XMT LVL (R9) on the front panel.
Monitor the output signal at the front panel through the XMT
test points.
FSK Modem IC
This integrated circuit is the central component of the 49013
subassembly. It handles all data functions such as modulation,
demodulation, and filtering. Internal clocking is controlled by
an externally connected crystal for stability.
87C51 Microcontroller
This integrated circuit is used to initialize and control the
modem chip.
Front panel test switch
This switch (TEST) grounds the RTS lead, causing data carrier
transmission.
It is used to turn on the DCD (Data Carrier Detect) of the
opposing (distant end) of the modem. As a result, each of the
modems is used to verify the presence of the data carrier. This
allows level adjustment without the presence of data.
Switch S2
Switch S2 reverses the RXD, DCD, RTS, and TXD leads.
CIRCUIT DESCRIPTION
UPDATED
