T V S 7 0 2 B   T H E O R Y   O F   O P E R A T I O N
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                          July 20, 1987



     T H E O R Y   O F   O P E R A T I O N

     The  TVS702B  is  a control board that plugs into one of the
auxiliary sockets of the GE Master II Repeater.  A TVS701B board,
with 702 version software,  is mounted on the 702 board, and pro-
vides most of the control logic. The 702  board  provides  speech
synthesis,  level  conversion,  and  audio  interface for the 701
board.

     Two connectors provide signal paths between the 701 and  702
boards.  The  J2 connector provides the normal 701 interface sig-
nals. The J1 connector provides a data and control bus  that  al-
lows the processor on the 701 to control the voice synthesis cir-
cuitry of the 702.


     Voice  synthesis  is  provided  by  a  General   Instruments
SP0256-AL2  integrated circuit. This circuit generates allophones
in response to processor commands.  The output of the SP0256 is a
digital  pulse width modulated signal. It is mixed with the morse
code signal (J2 Pin 13), and then filtered using R5, R6, C10  and
C11. The resulting audio is amplified by the LM386 (IC2), and de-
livered to the output pins. Voltage regulator IC1 is used to pro-
vide  an independent supply to the audio amplifier. When the syn-
thesizer is not active, Q3 is turned off by the processor to save
power.