25004Re: 8" of not working Floppy Disk.
- Apr 1 9:05 PMHi Bill,
I'm not sure I understand a "partial port assignment".
But you did give me new hope and off I went to check if there is a port conflict.
After studying the Data Seperator circuit, it's a very nicely designed circuit that corrects the data/clock if it finds 5 missing clocks (ie, Data 00h misread). This I see makes the 6 00's of the IBM format invaluable for the data seperator to be in sync with the right pulses.
Going into the 1771, I see clock pulses every 4uSec, I see data pulses every 8uSec (data pattern AA). The data is skewed by 2uSec.
To me, this all looks good going in.
Coming out, I scoped the Data Read strobe, it goes low for 1uSec.
The data from the 1771 is high for the first 200nSec, but it then goes low, which is a data 1 (to the CPU) after the 74LS368's.
This happens on all data lines, which fills the memory buffer with FF's instead of the AA's I expect.
The 200nSec, co-incides with the Data Request Line going low. This DRQ line goes high well before I read the port and then goes low about 200nSec after I read the data port. I've confirmed the Read, Chip Select, A0, A1 lines. I thought and double checked that I am reading the right port. The DRQ line going low convinces me that I have the right port.
I've tried a different 1771 chip, (not sure if either chip works really).
I'm at my wits end, once again... any ideas?
Time to buy more 1771's?
--- In firstname.lastname@example.org, B Degnan <billdeg@...> wrote:
> I am starting to think you may have a partial port assignment
> problem. Maybe someone who knows more about the 1771 and Tarbell can
> yey or ney this.
> At 01:40 PM 4/1/2012, you wrote:
> >Hi Guys...
> >I'm still banging away at this 8" Disk Drive.
> >One drive definitely has a problem with the read amp.
> >The other drive seems to work fine, but it's my controller card
> >that's giving the problem. Tarbell 1011.
> >The Data/Clk seperator isn't working most of the time on most of the
> >data patterns. But it does work some times when I record a track of
> >0AAH's. When it reads back, it either reads as AA's, 55's or FF's.
> >I can understand being off a bit and getting the 55's since there's
> >no syncronizing, but the FF's is what I get 3 out of 4 times I read
> >the same track. And if I write a track full of 0F0H's, then I only
> >ever get a bunch of FF's back, no matter how many times I read. So,
> >now my task has switched to understanding / repairing this seperator.
> >When I'm not reading the disk (and the head is not loaded), I get
> >the occassional data pulse from the disk, is this normal? Just noise?
> >Does anyone have any idea why Tarbell would use their own data/clk
> >seperator and not the one inside the WD1771 chip?
> >Thanks for your ideas!
> >Yahoo! Groups Links
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