Commodore Amiga A500 Technical Reference Manual page 51

INTERFACING TO THE This section gives the necessary information for interfacing t o the
6 8 ~
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 t o 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 1 3 5 degrees later
7M C1 XORed with C3* (7.1 5909Mhz)
DAC 7M shifted 90 degrees later
7 M
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 t o 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 t o get 7M
=
7.09379Mhz and C1
=
3.546895Mhz. A
special circuit
is
required t o take five fourths of C1 t o derive the PAL
colorburst frequency of 4.43361 875Mhz.
The following clocks are available a t the edge connector:
Name Pin Description
C3* 1 4 C3 inverted
CDAC 15 DAC equivalent
C1
*
1 6 C1 inverted
Note that 7M (the processor clock) is not available a t the connector;
it can be easily generated by:
C3* XNOR C1
*
=
7M equivalent