Date   : Sun, 12 Nov 2006 16:42:42 +1000
From   : bdevries@... (Bob Devries)
Subject: 5 1/4" disc on PC

Richard said:
> If I remember correctly, the controller simply asks the head to step in
> a particular direction; the amount of step is set in the drive itself,
> primarily by the stepper motor.

No, this is not correct. The step time value is set by the programme which 
talks to the controller chip and the controller (1770 or 8271) generates the 
pulse width timing and sends a step signal on pin 20 (*STEP) with the 
direction being controllerd by pin 18 (*DIR)


--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Richard Gellman" <splodge@...                   >
To: <bbc-micro@...               >
Sent: Sunday, November 12, 2006 2:46 PM
Subject: Re: [BBC-Micro] 5 1/4" disc on PC


> David Harper wrote:
>>> This is because the floppy controller in the modern PC cannot read the
>>> low density disks.
>>>
> See other thread current in hot debate :)
>> I am not convinced it has anything to do with this (despite the other 
>> debate
>> that is going on at the moment).
>>
>> It sounds to me like a stepping-speed problem. A 5.25" drive cannot be 
>> brand
>> new :-) and it might be that the stepper motor that moves the head cannot
>> cope with the speed it is being asked to move by the more modern BIOS.
>>
> If I remember correctly, the controller simply asks the head to step in
> a particular direction; the amount of step is set in the drive itself,
> primarily by the stepper motor. Some drives have jumpers (or links in
> BBC Micro parlance) and a very fine stepper that allow the head step to
> be adjusted for differing disk formats.
>
> When I tried using my drive with a PC, I had to change a jumper somewhat
> ironically marked "MS" to get it to work.
>
>> I do not know Omniflop well, and do not know whether this is an 
>> adjustment
>> that can be made within it. If it is, then it would be worth trying.
>>
>> You probably won't be able to adjust the stepping speed from the BIOS
>> settings in the CMOS - PCs are just not that flexible.
>>
> Neither is the floppy interface. The connection is low level type, i.e.
> it doesn't take commands or return result codes, etc. It has simple
> control lines such as step, step direction, track 0 sense, index sense,
> etc. This is what leads me to believe head step is configured in the 
> drive.
>
> There is one thing that makes think this might not be true, and that is
> the FDrive setting on the Master 128 (or keyboard links on the model B).
> This adjusts a head step time, but I believe this only allows to
> configure the machine to wait a certain period after issuing a step
> before assuming its safe to being operation again. I may be wrong on
> that though.
>>> If you can get hold of an older PC, possible one with an FDC that is a
>>> plugin board then that will be able to cope.
>>>
>>
>> I would agree that you should try it on an older PC (and if it won't work 
>> on
>> an old one, then throw it!) But if it will work on an old one, then I
>> suspect it is a BIOS rather than an FDC problem.
>>
> Put OmniFlop to use. Once the driver is installed it does improve the
> chances of reading a disk dramatically (in my limited experience). But
> you *may* still need to adjust the drive itself before it'll play nice
> with a PC controller (or at least the BIOS/OS trying to initialize it).
>
> -- Richard
>
>
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