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RAM-COMM Expansion Board 1
Interface Circuitry 1
Input/Output Handling 1
Expansion Board Schematic 2
RAM - COMM Expansion Board
The expansion hardware provides additional memory and
cow~~~ication capabilities for the AT&T UNIX PC. The
expansion hardware!s EIA ports make it possible for the PC
to communicate with another terminal or computer.
Additional memory and EIA capabilities are available
separately or in combination, as shown in the following list
of expansion hardware options:
0 O.SMB RAM Expansion Board (no EIA ports)
0 2.0MB RAM Expansion Board (no EIA ports)
0 O.SMB EIA/RAM Combo Board (two EIA ports)
0 1.0MB EIA/RAM Combo Board (two EIA ports)
0 1.5MB EIA/RAM Combo Board (two EIA ports)
0 Dual EIA Port Board (no RAM, two EIA ports)
The expansion hardware includes:
o An interface connection PI and associated
circuitry
o RAM memory
o EIA connection circuitry (if an EIA or Combo
board)
Interface Circuitry
All communications between the expansion board and the UNIX
PC bus are through the expansion board interface connector
Pl.
Input/Ou~ut Handling
As a direct memory access (DMA) device, data transfer from
the expansion board to the PC bus causes the 68010 to wait
while data is transferred into RAM memory. Data transfer is
considered a fast cycle (500 ns) .
1
Expansion Hardware
There are three functions which the expansion board may be
called upon to perform. Read to memory, read from memory
and port to or from memory to the RS-232 interface.
Expansion Board Schematic
Sheet 2--Memory Access Control Circuitry:
This circuitry consists of address latch 1K, lower and upper
data strobe control, consisting of demultiplexers 3H and 3J
and OR gates 3B and parity interrupt, 2C and 2E.
Sheet 3--Memory Bus Management and Communications Circuitry:
The upper portion of sheet 3 of the schematic contains map
address management circuitry consisting of multiplexers 4A,
4B, 4C, 4E, 4H, and 4J. The lower portion of sheet 3
contains the communication interface IC lIE, RS-232 line
drivers 12J, 12K, and 12A, and RS-232 receivers 11A and 12B
and port connectors J1 and J2.
Note
This circuitry is present only on the
EIA/RAM Combo and EIA/RAM boards. The
0.5 and 2.0 RAM expansion boards do not
contain interface circuitry or RS-232
ports.
Sheets 4, 5 and 6--Memory (RAM):
Memory circuitry consists of the X, Y, and Z bus, the read
bus and read bus control 1lH and IIC, and upper and lower
parity generator ICs 5K through 10K.
Depending on the amount of RAM that is mounted physically on
the expansion board, these locations mayor may not be used.
Sheet 5--Expansion Bus Interface:
The lower portion of sheet 5 of the schematic also contains
data transceivers IC and IE connected to the read bus and
expansion bus connector PI completing the expansion loop.
2
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