CTI Products TSAM Transmitter Steering & Audio Matrix - Manual (Page 71)

TSAM Installation and Maintenance Rev. 2.10 Chapter 8
CTI Products, Inc. Maintenance Theory
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8.2.2 Audio circuitry power supply
All audio circuitry uses a mid supply audio reference. This audio reference supply is 6.3 Volts with
respect to chassis ground. This reference is the audio ground. Care should be taken not to tie audio
ground and chassis ground together. This will short the audio 6.3V supply and severely distort all audio
signals. Do not clip the ground lead of a scope or other grounded test equipment to the audio ground.
Audio ground is denoted on the schematic by the triangular ground signal.
12.7 volts DC from the system supply feeds the IC137 rail splitter IC (IC210 on receive board). The
output of IC137 is a buffered low impedance 6.3V reference supply. This is the audio circuitry ground
reference. Op amp IC114 (IC209 on receiver board) provides an alternate 6.3V reference with degraded
performance. This circuit is not normally used.
8.2.3 Microcontroller Unit (MCU)
All operations of the TSAM are performed under control of the MCU (IC126). The TSAM uses a
Motorola 68HC11 MCU with external RAM (IC129) and ROM (IC128) for data and program storage.
The MCU has internal EEPROM memory for the storage of all programmable parameters. This reliable
form of non-volatile memory safely stores the configurable parameters when power is removed, without
requiring any backup power.
The address and data bus control logic consist of latch IC127 that is used to separate the multiplexed
address and data information from the MCU. Address decoding is accomplished by IC125 and IC124.
ROM is mapped from Hex address $8000 to $FFFF. RAM is mapped from $0000 to $7FFF.
The MCU integrates the following control functions:
• Serial Peripheral Interface (SPI) for control I/O
• RS-232 SCI interface for communications with programming terminal
• A/D converter used for factory test and diagnostics.
Serial Peripheral Interface BUS (SPI)
Most control inputs and outputs used by the MCU to control board level functions are accessed through
the SPI interface. This interface is roughly equivalent to a serial to parallel converter. Parallel I/O data is
converted to serial data then shifted into or out of the MCU. The MCU converts that data back to a
parallel form were it can be read or written to by the MCU's control program. In addition to parallel I/O,
other data is sent on the SPI bus. The MCU sends the frequency control data, for the keying tone
generators, over the SPI bus.
The following control logic and peripherals are connected to the SPI bus:
• Command shift register IC130, and SPI command decoder IC131
• Output register IC132, TX crosspoint, and RX crosspoint
• Tone generators 1&2, IC108 and IC109
• Input shift registers IC115-117, IC206-207 (provides 40 logic inputs)
The SPI system allows access to a large number of peripheral components without adding all the hardware
required to access peripherals through the traditional memory mapped processor bus.
The SPI command decode logic consists of a command shift register and a 22V10 PAL type device. This
device is programmed to perform SPI address and function decoding. The use of this device as an address
decoder allows the Master TSAM to control all of the TSAM peripherals on any TSAM attached to the
SPI bus. Expansion TSAMs do not require an MCU. The MCU only performs a low level diagnostics
when it is addressed as an expansion TSAM.