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MegaDisc 06 (1988)(MegaDisc Digital Publishing)(AU)[m][WB].zip
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ExpanBlues2
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1988-03-28
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61 lines
NOISY BUS ON A1000s
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ED. NOTE: For a locally devised modification that fixes this
problem, check the "PAL1.3to1.4.mod" article in OZ_PRODUCTS.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Amiga Community has rumbled for over a year with stories
of people who can't attach more than one non-terminating
peripheral device to the Amiga 1000 expansion port.
The negative experiences of many Amiga owners have led some
hardware manufacturers and developers to find out what was
keeping their peripherals form working correctly with some
Amigas and to come up with some low cost fixes.
As of this writing , most manufacturers feel that the
problem with the Amiga 1000 expansion bus - specifically
with its noisy data lines - originates on the daughter-
board that contains the Writeable Control Store (WCS).
One developer speculates that the WCS was a last-minute
addition to the 1000 because KickStart was not ready to be
cast into silicon when the Amiga was released . Commodore-
Amiga came up with the WCS so that KickStart chould be
upgraded easily (as happened twice) when it was debugged.
Independently, many people have discovered that two of
four PAL (Programable Array Logic) chips on the daughter-
board are not well Grounded. This makes the chips
susceptible to extraneous electronic noise. Others have
discovered that daughterboards that use Texas Instruments
(TI) PAL chips don't exhibit the same expansion bus
problems as the daughterboards that incorporate Monolithic
Memories Inc (MNI) PAL chips. It's not that the TI equipped
boards are less noisy , just that the chips appear less
affected by by electronic noise than the NMI PAL chips.
For months, C Ltd. has sold a PAL upgrade to customers
having problems with expansion devices. They remove two of
the MMI PAL's ( DPALCAS & DAUGCAS ) and replace them with
TI PAL's. Computer Systems Associates take a different tack.
For machines encountering bus problems, they recommend that
the four daughterboard PALs be Grounded together via a
jumper connecting pin 10 of each chip. Some Amiga dealers
take this step further by running a ground from negative
side of C1 electrolytic cap to secure a Ground like the
metal shelding that encases the Amiga motherboard.
For Amiga 1000 owners having trouble with peripheral
devices attached to the expansion bus, a PAL swap or
additional Grounding of the WCS daughterboard may be just
what the engineer ordered.
--RR
~~~~~~~~~~~~~~~~~~~~~~~~~ END OF EXPANBLUES2 ~~~~~~~~~~~~~~~~~~~~~~~~~