TB8100 Installation and Operation Manual Functional Description 43
© Tait Electronics Limited June 2005
The PMU behaves in a similar way to the PA.
The system control bus has been designed to operate only within the
TB8100 subrack. It has not been designed for use outside the subrack or to
interconnect two subracks.
I
2
C Signals The TB8100 BSS uses the I
2
C bus and a proprietary software protocol to
provide communications between any modules connected to the bus.
Typically this involves the reciter assuming ‘primary’ status, and PAs and
PMUs ‘secondary’ status. The reciter co-ordinates the entire subrack
operation, reading from and writing to all modules, including the control
panel. The I
2
C bus allows the reciter to perform the following functions:
■ monitoring (e.g. operating status, module details, operating temperatures
etc.)
■ diagnostics (execution of tests to confirm correct operation)
■ firmware upgrades
■ configuration (of operational parameters).
The I
2
C current source is located in the PMU so that the TB8100 BSS can
operate with the control panel removed. However, the PMU must be
powered up to enable the I
2
C communications to operate. Base stations
which use the 12V PA do not require a PMU, and in this case the I
2
C
current source is located on the dual base station subrack interconnect
board.
RS-232 Signals Service Kit, Alarm Center and Calibration Kit serial communications all
occur directly between the connected computer (or modem) and the reciter
over the RS-232 serial lines. When the connected computer needs to
communicate with the PA, PMU or control panel, the reciter routes the
RS-232 data stream to the I
2
C bus. Only reciters use the RS-232 interface.
Because RS-232 is a peer-to-peer physical interface, the control panel
converts RS-232 to open collector logic. Open collector logic allows a
single control panel to communicate with one or more reciters. This same
logic level conversion is also performed in the Calibration Test Unit when
the control bus interface is connected directly to the reciter.
Fan Signals The power and ground signals for the PA and PMU fans are routed from the
modules to the front panel (via the control panel) along the system control
bus. These signals are electrically isolated from all other system signals to
ensure fan noise is not transferred to other sensitive system components.
Protective diodes prevent the PA in one base station from being back-
powered by the PA in the other base station via the fan power lines.
In a dual base station, either PA can power the PA fan at any time. Thus the
PA that needs the cooling from the fan can control and receive it, while the
other PA will also be cooled even if it does not require it.
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