ACC RC-96 Owner's Manual page 114

Chapter Nine: How It Works
The audio switching and mixing circuits consist of two active
mixers, one for audio driving the repeater transmitter, and one
for audio to the phone line. Selection of active sources into each
mixer is supervised by the computer program in response to
normal repeater operation and user commands.
The logic outputs from the board for transmitter P1T and general
remote control functions are output ports buffered by high
voltage/high current (60 V, 500 rnA) VMOS PET transistors.
The logic inputs·are buffered by an integrated transistor array
which provides a universal logic lev:el compatibility.
The speech synthesizer (U23) mterfaces to the CPU through I/O
ports and is controlled by the microcomputer program. The pot
RI09 adjustment sets the synthesizer clock frequency, setting the
pitch of the voice.
The tone generator (U26) creates Morse code, courtesy tone, and
Touch-Tone audio under control of the computer program.
The Touch-Tone receiver (U14) may connect to any of the audio
input channels under control of the computer program. The
receiver detects Touch-Tone audio and sends the information to
the microcomputer to permit command evaluation.
The telephone interface provides the protective coupling between
the op amp audio signals and logic control signals and the tele­
phone line. It includes ring detect, off-hook control, impedance
matching, and isolation.
86 • RC-96 REPEATER CONTROLLER OWNER'S MANUAL