Re: [ti-99/4a] disk drive question....
- I reported the wrong HDC number! Inside my Myarc HFDC there is the same
chip you have (SMC HDC 9234). I am very sorry for the confusion I
Also, as you have already rightly guessed, I simply have the SMC FDC 9216,
not the *B* series.
I have never tried to connect an 1.44 MB 3.5" disk drive to my Geneve.
Do you think I should replace the 9216 with the *B* version?
What difference would the 9216 *B* make? My SMC 1988 Catalog says the
*normal* 9216 version is for 5.25" drives and the *B* version is for both
5.25" and 8" drives.
I must admit it would be nice to have a 3.5" drive installed in my Geneve,
but this is not the real reason why I am interested in the 1.44 drive.
What I am aiming to is to understand how the High Density (500 kbps
Transfer Rate) is implemented in a system.
Up to now, I used to think it depended on the floppy disk controller chip,
as it happens with FM and MFM. But now, I am beginning to suspect that the
controller chip has nothing to do with it. No FD Controller chip I know of
has an High Density option directly implemented in the chip itself. I
think that, as long as MFM is selected, the High Density (500 kbps
Transfer Rate) is enabled by a suitable clock speed of the FDC board.
In the SMC FDC 9216 chip (Floppy Disk Data Separator) there are two pins:
CD1 and CD0. By changing the status of these pins (0,0) you can change the
value of the internal clock divider circuit (the lower the divider, the
higher the frequency). Maybe, if you start with a frequency of the
Reference Clock (REFCLK) pin high enough, you may end up with the a
frequency suitable to obtain the 500 kbps (High Density Transfer Rate).
And, by changing again the status of the CD1 and CD0 pins (0,1), you could
halve the frequency, down to 250 kbps, suitable for Double Density.
Do you think the above is what really happens inside the Myarc HFDC?
The real reason I would like to know how High Density works on a floppy,
is that I would like to write a PC program to format a TI floppy disk.
Thanks for your support!
----- Original Message -----
Sent: Friday, December 01, 2000 10:42 PM
Subject: Re: [ti-99/4a] disk drive question....
> All (current) Myarc HFDC's have the "9234" chip on them! Do you
> use that card with a Geneve? I gather you would not be able to format
> 1.44MB floppies because of the wrong chip. If it is preventing you from
> formatting high-density disks, or you are having other problems because
> of it... maybe Tim Tesch could send you the correct chip?
> - Ken
> P.S. Does your HFDC have the 9216 "B series" of chip on it? You should
> have that on there, too! Chances are, that since you have the 9224
> (instead of the 9234)... you only have the 9216 chip (it's a small 8-pin
> chip). The 9216B will be clearly printed on the chip, if you have it!
> On Fri, 1 Dec 2000 17:17:25 +0100 "Paolo Bagnaresi @ Libero"
> <paolo_bagnaresi@...> writes:
> > <SNIP> I have a Myarc HFDC
> > (bought in 1988?). It uses an HDC 9224 controller chip, manufactured
> > Standard Microsystems Corporation. Apparently, this chip only handles
> > to Double Density (250 kbps). Is the High Density (500 kbps) a hidden
> > function of that chip or did Myarc make another version of the card
> with a
> > different controller chip? Or, finally, am I missing something?
> > Thanks,
> > Paolo
- "Dan Olson" <dano@...> wrote:
> A simple test would be to write the disk at what you assume is low250
> density, remove the disk from that machine, and attempt to read it in
> another which has a controller that it known to be capable of only the
> kbps data rate. This involves having access to that hardware.That would tell for sure whether (or not) those sectors have been
formatted in at 250 kbps.