INTERFACING TO THE
This section gives the necessary information for interfacing to the
68~
BUS
CONNECTOR
68000
bus connector on the left side of the Amiga A500 (or the
ON THE AMIGA
S00
right side of the A1
000).
THE CONNECTOR ON THE
AMIGA
The connector is a standard dual row
86
finger
(43
on a side) edge
connector, spaced on
.l" centers. Here are some part numbers of
connectors that are compatible:
solder tail AMP 2-53084
1
-
1
wire wrap AMP
4-530396-7
card extender AMP 1-530826-2
See accompanying drawing for physical dimensions of this connec-
tor on the
A500,
Figure A-3 in Appendix A.
TIMING
Clocks
For this discussion, see Figure 3.2.
The entire computer board is run synchronously to the
3.57954Mhz
color clock (Cl). This
is
accomplished by generating a number of
sub-multiple frequencies from our master
28.63636Mhz crystal os-
cillator. The following are the primary clocks on the board:
Name Description
C
1
The 3.579545Mhz Color Clock
C2 C1 shifted
45
degrees later
C3
C1 shifted
90
degrees later
C4
C1 shifted 135 degrees later
7M C1
XORed with C3* (7.1 5909Mhz)
DAC 7M shifted
90
degrees later
7M
is
the processor clock for the
68000
microprocessor. C1
-C4
and
DAC are used to clock the custom chips and for determining the tim-
ing of signals to the memory arrays.
The above frequencies are true for NTSC Amigas. A PAL Amiga will
operate slightly slower, with a main clock of 28.3751
6Mhz. This is
divided down to get 7M
=
7.09379Mhz and C1
=
3.546895Mhz. A
special circuit
is
required to take five fourths of C1 to derive the PAL
colorburst frequency of 4.43361
875Mhz.
The following clocks are available at the edge connector:
Name Pin Description
C3* 14 C3 inverted
CDAC
15
DAC equivalent
C1
*
16 C1 inverted
Note that 7M (the processor clock)
is
not available at the connector;
it
can be easily generated by:
C3* XNOR C1
*
=
7M equivalent
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