Datron TW7201I, Руководство пользователя

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4: Theory of Operation
TW7201I-MS 4-7
The DHSL modem transmits data in a 10-bit burst over a 2-wire line. Of the
10 bits, eight bits are digitized voice and two bits are data. The modem link is
synchronous. The two data bits are separated and stacked by two data set
interfaces (DSI) to give two digital channels. One digital channel provides
transceiver control; the other channel is a spare.
Power and
Ground Power and ground are routed from the Power Supply/Interface board to the
DHSL Modem board through the J2 connector. Connector J3 provides the
remote line interface and the front panel interface is through J1. Connector J11
is used for the accessory connector interface. Voltage regulators U14 (5 Vdc),
U17 (8 Vdc) and U12 (9 Vdc) provide regulated power to the various circuits.
Modem Clock Crystal oscillator Y1 (4.096 MHz) and associated logic (U10F, U10E, U10D,
U8 and U9) generate the modem clock that provides timing to the modem IC
U7, CODEC IC U11 and the two DSI chips U3 and U4.
RS-232 Interface The TW7201I can communicate with a DTE using RS-232 receiver/driver U5.
U5 provides an RS-232 interface to both accessory connectors. The baud rate
for the RS-232 interface is configured by the 8-position DIP switch S1 to 9600
through the data set interface (DSI) U3. DSI U4 provides a 9600 baud spare
data channel between the TW7201I front panel and the transceiver.
Alternatively, the spare channel can be used as a switch using Q6 as the
output. The input is set by the 3-pin header JU9 set to the BC position.
Codec The codec U11 is a voice digitization and reconstruction device. In transmit
mode, the TW7201I uses the codec to digitize audio signals from the front
panel microphone or an external transmit audio source connected to either of
the rear panel accessory connectors. U11 then sends this audio to the DHSL
modem U7 to transmit to the transceiver. In receive mode, the codec receives
digital information from the modem and returns it to audio signals that are
output to the front panel speaker through the Front Panel Processor board or to
an external speaker connected to either of the accessory connectors.
DHSL Modem The DHSL modem U7 interfaces with the transceiver across a 2-wire remote
line coupled through transformer T1. U7 receives from and returns digitized
audio to the codec U11. The modem receives digitized audio from the codec
and digital control signals from the front panel, then transmits them to the
transceiver and vice versa. It can also receive data from a DTE through DSIs
U3 and U4.
Receive Path The DHSL Modem board receives digitized audio from the transceiver
through the 2-wire remote line, then sends it to the codec to be decoded to
analog audio. The receive audio output from the codec is coupled via C30 to
the audio amplifier U13D, then output to the front panel speaker (SQA) via
output amplifier U15C. The receive audio can be routed to an external speaker
via the 600 ohm accessory connectors (600RXA) driven by amplifier U13C.
Refer to Figure 4-4 on page 4-9.