TB8100 Installation and Operation Manual Functional Description 55
© Tait Electronics Limited June 2005
Serial Service Kit communications are transferred from the attached serial
device (e.g. a personal computer running the TB8100 Service Kit), buffered
on the control panel and passed into the RISC’s UART.
Inter-module communications traffic (for example monitoring, diagnostics
and firmware download messages) is passed between the reciter and
PA/PMU via the I
2
C bus, which runs a Tait proprietary protocol. The
reciter acts as a router, in that messages to and from the PA and PMU are
passed through the reciter between the UART and I
2
C ports.
When each PA/PMU module powers up for the first time, it requests the
RISC, via the I
2
C bus, to allocate a unique address to that module for use
across the I
2
C bus. Each module on the I
2
C bus must have a unique address.
The reciter assumes ‘primary’ status, while all PAs and PMUs assume
‘secondary’ status. Consequently, the reciter polls modules and the modules
reply, forming a poll-response architecture with unique addresses and
associations.
There is no information passed over the system control bus that is real-time
dependent. All real-time processing needs, such as fault recovery for all
modules, are supported by the microprocessor present in each module. The
only real time signal in the system is the PA_KEY signal that is passed
between the reciter and the PA. This signal is a critical part of the TX_KEY
ramp up and down operation and is summed with the exciter RF output to
the PA over the coaxial interconnection cable.
For example, when a TX_KEY signal is passed to the reciter system
interface board, the following actions occur:
1. The TX_KEY signal is read and processed by the RISC
microprocessor which, depending on the configuration and status of
the reciter, will then initiate a transmission.
2. The RISC will instruct the DSP via the host port to initiate a
transmission and start modulating the RF carrier.
3. The DSP will enable the PA_KEY line to the PA microprocessor.
4. The PA microprocessor will then initiate a controlled PA output ramp
up.
Depending on the channel selected for the transmission, the RISC will also
re-configure the synthesizer as required, though this does not automatically
occur at the start of a Tx/Rx event.
At an appropriate time, the reciter’s RISC processor will poll the PA and
PMU modules for their status (including any alarm conditions) and process
the results accordingly. Whenever a user selects a PA/PMU monitor or
diagnostic screen in the Service Kit, the information is read from that
module via the I
2
C bus. It is then transferred through the RISC and passed
to the Service Kit computer using the Tait proprietary Service Kit protocol
over the serial port.
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