Adaptec and DMA (long)

[Bruce R. Larson]

In article <1990Nov02.021739.9280 at ddsw1.MCS.COM>, nvk at ddsw1.MCS.COM (Norman Kohn) writes:
> There have been many comments about boards that won't support
> the Adaptec 1542[AB] SCSI bus master controller.
> ...
> Timing and/or DMA problems on the motherboards have usually been blamed.  
>
> [ lots deleted ]
>
> I spoke with another board vendor last night and got another interesting
> comment.  He claims that the problem lies in the 1542B, which
> allegedly sits on the bus too long during boot-up.
> ...

I've just had an experience that suggests the 1542B is at fault.

SUMMARY
Erratic behavior with a 1542B, went away after installing a 1542A.

THE PROBLEM
I just sold a 386/33 cached Computer (by Caliber) to a client,
but they witnessed erratic behavior after installing a 1542B
and a Wren VI HH with ISC 2.2 pre-loaded.  For the record, the
1542B passed the busmatering test with flying colors (g=dc00:9).
Here are some of the odd things I witnessed.

i)   With all of the boards removed except the 1542B and a monochrone
     video adapter, the monitor frequently refused to display anything
     until the reset button was pressed a number of times.
ii)  whether the monitor would work at all was influenced by the relative
     positions of the video card and the host adapter.  In most config-
     urations it just did not work.
iii) The system would not even go through its memory test when the
     serial/parallel card was present.  (No, there weren't any IRQ
     or base i/o address conflicts.)

These sound like timing problems to me.

THE SOLUTION
I remembered a posting in this group (thanks again guys) about
possible problem when using the 1542B.  I replaced the 1542B with
a 1542A and every problem vanished.  I discovered this last night,
so I haven't had a chance yet to fax the info to either Adaptec or
my Adaptec supplier.

> 
> -- 
> Norman Kohn   		| ...ddsw1!nvk
> Chicago, Il.		| days/ans svc: (312) 650-6840
> 			| eves: (312) 373-0564

Bruce R. Larson
Integral Resources, Milton MA
Internet: ires.com!blarson at cs.umb.edu
Uucp:     ..!cs.umb.edu!ires.com!blarson
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