P74x/EN FD/N
1, P742, P743
(FD) 9-
2.3 Communication board
The communication board looks like the coprocessor board. The Differences are:
• Four duplex optical channels are provided.
• The second interconnection bus is not provided. The communication board controls no
board.
This board is only used within P741 relay. It performs the communication with the P742 and
P743 relays.
Up to 7 communication boards can be interfaced within P741 relay. So up to 28 P742 or
P743 relays can be interfaced from a P741 relay.
2.4 Internal communication buses
The relay has two internal interconnection buses:
• The first is controlled by the main board. Via its interconnection bus the main board
controls the coprocessor board (P741, P742 & P743) and the IRIG-B board (P741 only).
• The second is controlled by the coprocessor board. Via its interconnection bus the
coprocessor board controls relay boards (P741, P742 & P743), opto boards (P741, P742
& P743), input module (P742 & P743) and communication boards (P741).
These two interconnection buses are very similar. Both are based on a 64-way ribbon cable.
The ribbon cable carries the data and address bus signals in addition to control signals and
all power supply lines. Operation of the bus is driven by the main processor board that
operates as a master while all other modules within the relay are slaves.
The DSP processor has a built-in serial port that is used to read the sample data from the
serial bus. The serial bus is also carried on the 64-way ribbon cable.
The main part of the buses is a parallel link with 6 address lines for board selection, 16 data
lines and control lines. On the main controlled bus, main board drive address and control
lines. On the coprocessor controlled bus, coprocessor board drive address and control lines.
Other parts of the buses are:
• The sample serial link from input module to coprocessor board which loads analogue
channel samples.
• Power supply which are directly wired between the two interconnection buses.
• Serial lines for rear RS485 communication which are also directly wired between the two
interconnection buses. So in any way main board keeps control of the rear RS485
communication.
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