Floppy controller questions
ajp166 at bellatlantic.net
Tue Aug 23 16:16:23 CDT 2005
>Subject: Re: Floppy controller questions
> From: ard at p850ug1.demon.co.uk (Tony Duell)
> Date: Tue, 23 Aug 2005 20:15:48 +0100 (BST)
> To: cctalk at classiccmp.org
>> > 1) How do you vary the read/write data rate? Some 3.5" formats use MFM at
>> >250kbits/sec, others use MFM at 500kbits/sec. What relation does the WRITECLK
>> >input have to the data rate of the MFM-coded signal at the WRITE DATA output?
>> >What about the 8MHz master clock?
>> BY prescaling the clock. Master clock drive the internal cpu and
>> after prescaling the various timers (step rate, Head load time,
>> head unload time) Possible useful rates for Clock is 8 and 4mhz.
>> Use 8MHZ for fastest step rates, 4mhz for those drives (like sa400)
>> that need really slow step rates. Also the rate that the master
>> status register is updated is affected due to internal microprocessors
>> Write clock sets the write data rate and should corrospond to the
>> rate needed for media. Writeclock is 2x data rate. The master clock
>> is not synchronous to the write clock though it's easiest to derive
>> both from the same master source.
>To avoid confusion. I think it would be clearer to say that Write clock
>_need not be synchornised_ to the master clock. As you go on to say,
>there is no problem if Write clock is derrived by dividing down the
>master clock signal (asusming that will give the data rate you want), in
>fact just about every floppy controller board does it that way.
Err, I said that, did I not?
Two people seperated by a common language.
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