Conference 7.286::atarist

    It's possible that the drive select signal going to your second
    drive is bad (ie: always asserted).  All the other signals are
    identical between the two drives.
    
    If the drive select line was stuck asserted it would cause trouble
    with the other drive (drive A:). I would guess that drive B: (the
    CUMANA) would work fine even with the drive select stuck, but I
    could be wrong on that.
    
    You might try reseating all the socketed chips inside the ST as
    that seems to be the number one cause of most problems with the
    ST. I had to reseat my chips recently because I started getting
    the "..data may be damaged on drive.." error message on good floppies.
    
    If you have a local ST dealer he may be willing to connect a second
    drive to your ST in the store just to see if it works or not.
    
    	Ray

    
    
    Thanks for the response, suspected myself the permanent asserted
    SELECT line, but I have allready done what you suggested, ie take
    it along to my local friendly ST dealer, with some even more
    interesting results.
    
    The CUMANA works fine in his ST, no problems seen at all, both DRIVE
    "A" and "B" useable.
    
    A different 1M drive which the dealer had, a MICRO P I think, works
    fine in my System Unit, again both DRIVE "A" and "B" useable.
    
    The CUMANA still does not work in my ST, this starts to smell of BUS LOADING
    type problem.
    
    Does anyone know if the DRIVE BUS is fully Parallel or are any of
    the signals DAISY CHAINED, and therfore RE-DRIVEN by the DRIVE "A"
    LOGIC. If this were the case then the problem could be DRIVE "A".
    
    Anyone got any experience putting together home-brewed externel
    drives, in particuler using CHINNON units, this is the unit used
    inside the CUMANA.
    
    I am going to take my System Unit and CUMANA down to the dealer from
    whence the CUMANA came. They say they have CUMANA's working fine
    on there 520, 1040 amd MEGA System Units, I dont doubt it if it
    is a marginal loading problem, or even the posibility that their
    CUMANA's have other Manufacturers Drive Units in them. Will let
    you know the result.
    
    Ray, would try the CHIP RESEAT, but can I get easy access to the
    CHIP's without giving the game away, ie the System Unit is still
    under warranty, are their any seals inside that would show that
    someone had been this way before...
    
    Nat.G.
    

I have connected a 5.25" drive to my 1040 STF. It works fine, but some
signal lines had to be buffered because of termination problems. If you are 
interested in some more information , let me know.

Hans

    re .2
    
    There are two select lines, wich should allow for four drives.
    However the Atari scheme is different. Only two drives are allowed.
    All drive must be jumpered as to pretend to be drive 0.
    The two select lines on the bus are called select A and select B.
    The trick is that on the atari drives, the select B on the input
    connector is connected to the select A on the output connector.
    
    +--------+ select B       B+-------+	      B+-------+
    |        |-----------------|----+  |               |----+  |
    | 520 ST | select A       A|    |  |              A|    |  |
    |        |-----------------|-+  +--|---------------|-+  +--|
    +--------+                 | |     |               | |     |
                               | 0     |               | 0     |
                               +-------+               +-------+
                                drive A                 drive B
    
    With that scheme, the atari drives are interchangeable and the
    first in the chain is always drive A. If you have a CUMANA
    without an output connector, it will always be drive B.
    
    Now if your select B line is always asserted, your system might
    behave as you described in the basenote, i.e. select lamp on,
    and problems on drive A as both drives try to drive the lines at
    the same time.
    
    If you then take the CUMANA out, everything works fine. If you
    connect the CUMANA only, it will certainly work perfectly.
    
    The only way to be sure is to check the select lines with scope
    or DVM. The select B line is normally driven by the YAMAHA chip.
    (at least on the 1040, apparently some spare registers have been
    used.)                   
    
    BTW, it is NORMAL that both spindle motors go on at the same time
    when accessing either drive.
    
    re .3
    
    For those who want to install their own drive, 3.5 or 5.5, it is
    advisable to remove the bus termination resistor-pack from the drive.
    And keep the cables short...