23 Aug
2005
23 Aug
'05
12:15 p.m.
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
speed.
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.