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The 68000
transmits data
and control
to
and from
the peripherals
via the
parallel
110 and
the
3 custom chips
.
1M
is the processor clock to the 68000
.
Cl
,
C3
and
CDAC
are
used
to
clock the
custom chips and
determine the timing
of signals to
the memory
arrays.
ROM
The ROM
contains the kernel and
DOS routines
;
it
is
128K
x
16.
Parallel I/O
The 2
mUltipurpose
8520 110 chips
provide the
following:
110 to and from the
parallel port
connector
Control
lines to
and from
the joystick/mouse ports
A control
line
to
the front panel LED
Internal
control
lines
Keyboard
control
lines
,
clock
and
data
Serial
port
control
lines
Floppy
disk
interface control
lines
Internal
timers
These
2 chips reside on
the
68000
buses
and are
read
and written
by the
68000.
Clocks Generator
The
entire computer
board is run
synchronous to the 3.579545
MHz
color clock.
This
is
accomplished
by
generating a
number
of submultiple frequencies from
the master
28 .63636
MHz NTSC
(or 28.37516
MHz
for
PA)
crystal oscillator.
All
clocks
are generated by
the
Fat Agnus custom
chip.
The following are
the
primary clocks:
CI
3.579545
MHz
color
clock
C3
C2 shifted 45
degrees later
7M
C
I XORed with C3
=
7.15909 MHz
CDAC
7M
shifted 90
degrees later
Technical Reference
A-13
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