ACT apricot - Pin Detail

EXPANSION SLOTS
Pin Detail
Both Expansion Slots are 64-way connectors (DIN 41612,
2 by
32 female, with a type B housing) and are identical with
regard to the connections to the system buses, as illustrated
on the diagram of the Expansion Connector. A description
of each connection to the System Board is detailed below.
DBO - DBIS 16-bit system data bus. Connected to the
pair of transceivers which form the interface
between the processors and the system data
bus. DBO is the LSB, DBIS the MSB. In effect,
the bus is divided into two parts (the low
order section DBO to DB7, and the high order
sectionDB8 to DBlS), to support both 8-bit
(byte)
and 16-bit (word) data transfers. Byte
transfers
from/to even address locations are
transferred on the bus lines DBO to DB 7 and
byte transfers from/to odd address locations
are transferred on bus lines DB8 to DBIS.
Word transfers from/ to even addresses are
transferred on bus lines DBO to DBIS in a
single operation. Word transfers fromlto odd
address locations are automatically
transferred in two consecutive data byte
transfer operations; the first operation uses
bus lines DB8 to DBIS (odd address transfer),
and the second operation use bus lines DBO
to DB7 (even address transfer).
ABO - AB19 20-bit system address bus. Connected to the
octal D-type latches which demultiplex the
20 address bits from the local bus of the
multiprocessors (time multiplexed address/
data bus for the 16 LSB and the time
multiplexed address/status bus for the
4MSB). ABO is the LSB, AB19 the MSB. ABO
has a special function and is normally used
in conjunction with the BHE signal to
condition circuitry for byte or word data
transfers.
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