Tait TB8100 - Page 48

48 Functional Description TB8100 Installation and Operation Manual
© Tait Electronics Limited June 2005
possible clock interference from unlocked clock sources, generating
interference or deaf channels.
Direct Signal Paths It is possible to bypass a lot of the signal processing within the DSP on both
the Tx and Rx paths via user configuration. The demodulated audio signals
can be fed directly to the output CODECs, and the transmit CODEC
inputs are connected directly to the modulator. This allows wide band
audio signals to be processed via external equipment, if required, without
the DSP overheads usually needed for path A and B audio processing.
Digital I/O The bottom of the reciter section of Figure 4.10 shows the time-critical
RX_GATE, TX_KEY and COAX RELAY signals that interface directly
with the RISC. Less time-critical signals, such as digital I/O, interface to
the RISC via a synchronous serial I/O interface.
Module
Communication
Paths
The reciter RISC supports two main inter-module communication paths:
an asynchronous (RS-232) path to the control panel and a synchronous
(I
2
C) interface to all other modules and the control panel. Both of these
paths are interconnected via the system control bus cable on the front of the
modules.
The RS-232 signals from a connected computer or modem are buffered and
sent to the reciter on-board UART via the system control bus. The system
control bus uses an open collector TTL interface.
The inter-module I
2
C bus provides a path for the RISC to communicate
with all other modules and the control panel. This supports module alarms,
diagnostics, monitoring and control panel LED/keypad traffic.
The Power
Management Unit
(PMU)
The PMU section of Figure 4.10 shows the major functional blocks of the
PMU. Each converter is under the control of the PMU microprocessor,
which is also under the control of the reciter RISC processor via the I
2
C
communication path.
The high current DC-DC converter and high efficiency standby card are
both powered directly from the DC input. This means that the high power
DC converter can be switched off to conserve power when not transmitting
during modes.
The HVDC control and microprocessor card also provides current sources
(effectively pull-up resistors) for the system control bus I
2
C inter-module
communications path.