59
4.20 Barbus interface
The Barbus interface shown in Fig. 30. is based on the MPU6 board and is connected to the
MUX5 board via a red 11-way BARBUS connector having a keyway at pin position 7.
The Barbus provides a +34V supply for lamps and a +12V supply for electronics; these
supplies are protected by on-board fuses.
Because the MUX5 board does not r24V and -12V supplies, and is also a slave on
the Barbus, the +24V and -12V inputs are replaced by board address connections. Board
addressing functions are described in Sect. 3.6. The on-board CPU reads the trinary ADD0
and ADD1 inputs, which can either be floating at +2.5V, else linked to +5V or 0V to give 27
possible address combinations. Address links, which are fitted to the free connector at the
factory, may be any of those shown in Fig 2. The address links which are fitted are machine
specific and are shown in the relevant Machine Manual.
The +5V used for board addressing is tapped from the regulated Vcc supply, which is
obtained from the +12V supply by a 5V monolithic voltage regulator.
The 2-wire RS485 data link is controlled by a /TXEN signal from the on-board cpu which sets
it to send or receive COMMS+/COMMS– data at rates up to 100Kbytes/sec. At switch-on the
serial link monitor circuit produces a short low-level /RESET pulse to initialise the cpu, after
which the RX line of the RS485 serial link is continuously monitored. If the RX line remains
low to indicate a "break" situation, the CPU is reset.
11
10
9
8
5
6
4
3
2
1
KEY
+5V Regulator
2A
5A
BARBUS
0V
+12V
+34V
MUX5
board
RS485
+5V
0V
TXEN
RX
TX
COMMS-
COMMS+
Vcc
ADD0
ADD1
MUX5
board
cpu
Monitor
RESET
+5V
Typical links
Fig. 30 MUX5(E) board Barbus interface