13 Oct
2015
13 Oct
'15
5:04 p.m.
On 10/13/2015 5:08 PM, Jay West wrote:
Pictures of the S/130 system I'm building up are
at
https://www.flickr.com/photos/131070638 at N02
I think the last I posted here... the cpu was up and running, that was the
first piece I refurbished. I took everything out of the rack and cleaned
that up well, and the cpu has been remounted there.
Yesterday I mounted the 6030 dual 8" floppy drive. It was squeaky clean
inside and at power up everything does what it should. However, I can't
proceed further with it as I have no media. The docs say it uses hard sector
8" floppies, which I believe I can find. However, it specifies 8
sectors/track hard sector floppies - and those I've never heard of. Maybe DG
made them special just for their gear, or, maybe the drive or controller or
software was smart enough to expect the more common 32 hard sector floppies
and knew to only pay attention to every 4th sector hole ;)
I see that sector count (0-7) in the 6030 technical reference.
But all of the HS floppies I have for DG are 32 sectors - and many of
those are software distribution floppies for Novas, appropriate to the
6030. They are all labelled DG Diskette (as opposed to /2, /3 or /4),
as per the illustration in the 6030 manual.
SO:
The manual specifies a max sector access time of 166ms, and a min of
1.2ms. 166ms implies a rotational speed of 360 rpm (6 revolutions per
second, or 166ms).
Divide that by 8, and we get sectors about 20ms apart (8 sectors), with
an extra index pulse 1/2 of that, or 10ms.
For 32 sectors they would be at 5.1ms and the extra index pulse would be
1/2 of the 32 sector pulse, or 2.6ms.
Looking at the schematic I have, 001-000797-10 (rev 10), sheet 2, bottom
left quadrant, the index pulse is fed into a one-shot with a time
constant noted of 3.9ms to generate the index pulse - which would be
pretty darn close to 1/2 of the way in between 2.6ms and 5.1ms.
The sector pulse is derived from a counter, U63. The counter has an
input signal labelled "DIV 4" to pins 5 and 6.
Also (this would have saved time had I seen it right away) there is a
timing diagram, 001-000893-00 that shows 5.2ms between sector pulses,
and 2.6ms for the extra index pulse, with pulses being 1.1ms in length
and also shows the 3.9ms one-shot timing.
That cinches it: the design is for 32 sector floppies.
More to follow related to my hardware and software inventory, but I just
got called to dinner.
JRJ