ROM
The
system
board
supports
both
Read
Only Memory
(ROM)
and
Random
Access
Memory
(RAM).
It
has space for up
to
512K
of
~
ROM
or
Eraseable Programmable
ROM
(EPROM).
Six module
sockets are provided,
each
of
which
can
accept
an
8K
or
8 byte
device. Five sockets are populated with
40K
of
ROM. This
ROM
contains
the
cassette BASIC interpreter, cassette operating
system,
power-on
self test,
Input/Output
(I/O)
drivers,
dot
patterns for 128 characters in graphics mode,
and
a diskette
bootstrap
loader.
The
ROM
is packaged
in
28-pin modules
and
has
an
access time
of
250-ns
and
a cycle time
of
375-ns.
RAM
The
RAM
on
the system
board
is as shown in the following chart.
System
Board
Minimum
Maximum
Memory
Soldered
Pluggable
Storage Storage
Modules
(Bank
0)
(Bank 1-3)
64K
by 1 Bank 3 Banks
64/256K
64K
256K
1
Bit
of
9
of
9
Memory greater
than
the system
board's
maximum is
obtained
by
adding memory cards in the expansion slots. All memory
is
parity-checked
and
consists
of
dynamic
64K
by
1 bit chips with
an
access time
of
250-ns
and
a cycle time
of
410-ns.
DMA
The
microprocessor is supported by a set of high-function support
devices providing four channels
of
20-bit
direct-memory access
(DMA),
three 16-bit
timer/counter
channels,
and
eight
prioritized interrupt levels.
System
Board
1-13
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