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4.12 SP/Diff (Audio)
The SP/Diff port is designed to provide stereo digital sound through the machines speakers,
as well as the facility to receive audio signals from other sources such as from a PC.
4.13 Barbus interface
The proprietary Barbus is a combined power bus and serial data link connected in a daisy
chain layout between the machine modules as shown in Figure 2. The Barbus is connected
to the MPU6 board via a red 11-way BARBUS connector as shown in Fig. 24, the connector
having a keyway at pin position 7.
Power bus lines are input as shown, the +34V and +12V lines being fused. +5V for the
MPU6 circuits is obtained from the +12V line, using a monolithic voltage regulator. The +5V
line is protected by a crowbar circuit in case a faulty voltage regulator should attempt to place
an excessively high voltage on the line, in which case the crowbar operates to blow the fuse
and disable the power line. The -12V is provided to supply a Datapak when required, the
+24V is used by the Coins and Hopper/Slide interfaces.
The 2-wire RS485 data link is controlled by a BARBUS_DIR signal from the MPU6 which
sets it to send or receive COMMS+/COMMS– data at rates up to 100Kbytes/sec.
4.14 Back-up battery
A back-up Lithium 3V battery and associated battery manager are provided to maintain the
contents of the static RAM when the machine is switched off. The battery manager monitors
the +5V supply and switches in the battery when the supply has dropped to +2.4V. In this
situation the back-up battery also powers the on-board processor to function at a reduced
status.
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