Option Interface Board, Speech Processor

RTU-292 Operations Manual

Bus drivers U60 and U61 are the input devices for the front panel switches; latches U62 and U63 light the front panel LEDs. Latches U50 through U53 send control signals mainly to the audio circuit sections. U56 and U57 send inputs to the data bus; U54 and U55 read Option switches SW1 and SW2. Keypad decoder chip U59 provides the keyboard interrupt and translates keypad closures before sending them onto the data bus via latch U58.

4.3.9PROMPT TONE GENERATOR

Timer IC U30 can create tones of 500, 600, 750 or 1kHz, depending on the states of control signals from the CPU Board DT0 and DT1. The volume of these prompts may be adjusted via potentiometer R158. U33B, U33C, and U33D route either tone prompt or voice prompt signals to the circuitry; controlled by the T/V signal from the CPU.

4.4 OPTION INTERFACE BOARD

This board contains the basic databus, power audio, and control lines to operate the various options that may be installed on the unit on the options tray. See figure 8-4.

4.5 VOICE PROMPT OPTION

The Voice Prompt Option outputs prerecorded voice prompts into the telephone send signal or into the radio transmit audio output from the RTU-292. See figure 8-5.

4.5.1 SPEECH PROCESSOR

The heart of the voice prompt option board is the speech processor chip, U7. This chip is an ADPCM (Adaptive Pulse Code Modulation) processor containing built-in A/D and D/A, and can be used for recording as well as playback. The digitized voice prompts are contained in EPROM U5, which U7 accesses via data bus AD. The prompt analog audio is output on U7-28 and is passed through amplifiers U9 and U10. These amplifiers are arranged as a five-pole active low-pass filter which removes remnants of the 8 kHz sampling frequency from the output audio.

4.5.2 CONTROL PROCESSOR

The control microprocessor is the 68HC11A0, an 8-bit processor running at 8 MHz with a basic instruction cycle time of 2 microseconds. There is some I/O from the processor chip itself from Port D (pins 20 to 25) and Port A (pins 27 to 34) which controls the Audio Processor chip. The control input to the board is to Port E (Pins 43 to 50) from connector J1. The lower eight bits of the address bus are separated from the data bus by address latch U2.

EPROM U4 is the program memory, a 27C256 providing 16k of address space. Chip select signals for the various I/O are provided by PEEL U6.

Several devices on the CPU board use a 3.58 MHz clock signal that is provided by crystal Y2 and gates U12B and U12C.

U3 is a reset generator that ensures an orderly power-up sequence for the microprocessor and associated components. It senses the voltage on the +5V line and generates a reset while the voltage is below approximately 4.55V. As the voltage rises above the threshold, a delay is generated by C4 to insure processor clock stability before operation commences. Resistor R5 prevents resetting on short spikes on the 5V line.

4-25	JPS Communications, Inc.