12 Aug
2015
12 Aug
'15
2:12 p.m.
I forgot to mention one item. Since I had VERY few Double Sided
media with the index hole offset that extra 1/2" from the Single Sided
index hole - and I have many RX02 compatible floppy media which
are Single Sided with the index hole in the wrong place for being a
Double Sided media - I added a DPDT switch to the sense circuit
of the DSD 880/30 drive. In the normal position, the Single Sided
floppy media are detected as Single Sided floppy media. In the
opposite position, a Single Sided floppy media is detected as Double
Sided and the DSD 880/30 is then able to read / write both sides
of the floppy media. Since the DSD 880/30 is also able to perform
a LLF (Low Level Format), I am able to use all of the RX02 media
as Double Sided WITHOUT the inconvenience of having to punch
the extra index hole.
Jerome H. Fine wrote:
Josh Dersch
wrote:
Here at the museum I'm evaluating the use of
a SuperCard Pro
(http://www.cbmstuff.com/proddetail.php?prod=SCP) to archive and
duplicate 8" floppies from various machines. It's not technically
supported (the manual states that it *should* work but has not been
tested, etc.) The disks I'm reading are nothing exotic (They're
standard double-density, double-sided disks with an IBM format -- I
could use a PC and ImageDisk to do the job, but the SuperCard is very
convenient, in theory...)
Thus far I've been successful in creating images of floppies, but
less successful in writing them back out. Thus far I've tried a pair
of Shugart 851s and a Qume QumeTrack 842. I'm using a DBit FDADAP
(http://www.dbit.com/fdadap.html) to deal with cabling and the TG43
signals. (And the 851s are jumpered properly for the TG43 signal, as
far as I can tell). I've also tried a variety of media (Verbatim,
Maxell) with the same results (though the position of the bad data
varies from attempt to attempt).
The issue is that upon reading back a disk that has been written via
the SuperCard, data is fine up until about cylinder 60, at which
point bad sectors start appearing more and more frequently (though
most of the data is still OK). I tried disabling TG43 just to see if
it made a difference, and it does - with TG43 disabled sectors
written past cylinder 43 read back as garbage.
I'm running short of ideas. Anyone else have any experience with
this combo? Any suggestions on troubleshooting tips?
I doubt that this suggestion will help, but it might be
useful for what are called RX03 compatible media.
The RX02 drive from DEC was emulated in hardware
by DSD (Data Systems Design). DSD Produced a
drive which was named the DSD 880/30 which consisted
of 3 * RL02 internal drives and a single floppy drive which
could read IBM Single Density and DEC Double Density
floppy media. The DEC names for those two floppy media
were RX01 and RX02. The actual DEC RX02 drive was
able to read in both Single Density and Double density modes.
In the case of the DEC RX01 and DEC RX02 drives, they
were both Single Sided. Further DEC did at one point intend
to support a Double Sided drive which I understand was to
be called the DEC RX03, but it was never released that I
ever heard about. The software support was specifically
included in V04.00 of RT-11 in the file DY.MAC, but was
probably never tested since the code was incorrect. By
V05.00 of RT-11, DY.MAC no longer contained the extra
code to support Double Sided media.
DSD extended the support and the DSD 880/30 contained
an RX03 compatible drive which could read Double Density
Double Sided media. What I don't know is IF the physical
characteristics of the Double Density media which DEC and
DSD supported are identical to the Double Density physical
characteristics of the floppy media to which you refer as having
"an IBM format" since I have never encountered any floppy
media from IBM other than Single Sided / Single Density.
To make matters simple IF the floppy media which you have
are compatible with DEC RX02 Double Density format, then
with the DSD RX03 floppy drive, I extended the DY.MAC
file for RT-11 and it now supports reading a Double Sided /
Double Density floppy mounted in a DSD RX03 drive. If
you can manage to locate a DSD 880/30 and controller to
run on a DEC PDP-11/73 with RT-11, then I can make the
DYX.SYS device driver available. To first make sure that
everything will work with the DSD 880/30, you can test your
floppy to see if a DEC RX02 can at least read the first side of
your floppy.
Please let me know if you know the answer to if your Double
Sided / Double Density floppy media are DEC RX02 compatible
on at least the first side. If that is true, then the DSD 880/30
drive will probably be able to read both sides very easily.
If you have any questions, please ask.
Jerome Fine 
12 Aug
12 Aug
3:36 p.m.
On 08/12/2015 11:12 AM, Jerome H. Fine wrote:
I forgot to mention one item. Since I had VERY few
Double Sided
media with the index hole offset that extra 1/2" from the Single Sided
index hole - and I have many RX02 compatible floppy media which
are Single Sided with the index hole in the wrong place for being a
Double Sided media - I added a DPDT switch to the sense circuit
of the DSD 880/30 drive. In the normal position, the Single Sided
floppy media are detected as Single Sided floppy media. In the
opposite position, a Single Sided floppy media is detected as Double
Sided and the DSD 880/30 is then able to read / write both sides
of the floppy media. Since the DSD 880/30 is also able to perform
a LLF (Low Level Format), I am able to use all of the RX02 media
as Double Sided WITHOUT the inconvenience of having to punch
the extra index hole.
My drives are configured to take either index signal--so it doesn't
matter if the media is coded as SS or DS. Many floppy drives can do this.
--Chuck
4:05 p.m.
On Wed, Aug 12, 2015 at 1:36 PM, Chuck Guzis <cclist at sydex.com> wrote:
My drives are configured to take either index
signal--so it doesn't matter
if the media is coded as SS or DS. Many floppy drives can do this.
Some 8-inch double-sided drives don't care about which index sensor is
active, other than to output the appropriate logic level on the TWO
SIDED interface signal, but will let you read and write both sides of
single-sided media.
Some drives, like the Mitsubishi M2896-63, can be configured to
suppress the READY output if the second side of a single-sided disk is
selected, or to ignore the sidedness of the medium. Mitsubishi refers
to this as "Ready Standard" vs. "Ready Modified".
4:26 p.m.
On 08/12/2015 01:05 PM, Eric Smith wrote:
Some drives, like the Mitsubishi M2896-63, can be
configured to
suppress the READY output if the second side of a single-sided disk
is selected, or to ignore the sidedness of the medium. Mitsubishi
refers to this as "Ready Standard" vs. "Ready Modified".
...and others, such as the Siemens FDD-100 (single sided) will output an
"illegal medium" signal if double-sded floppies are inserted.
--Chuck
5:22 p.m.
On Wed, Aug 12, 2015 at 2:26 PM, Chuck Guzis <cclist at sydex.com> wrote:
...and others, such as the Siemens FDD-100 (single
sided) will output an
"illegal medium" signal if double-sded floppies are inserted.
Interesting. I think the single-sided drives I've dealt with just
never assert READY, because they don't have a sensor at the index
position of a double-sided medium.
7:21 p.m.
On 08/12/2015 02:22 PM, Eric Smith wrote:
On Wed, Aug 12, 2015 at 2:26 PM, Chuck Guzis
<cclist at sydex.com>
wrote:
I could have that reversed--and that SS media in the FDD-200 would cause
an "illegal media" signal to be asserted, but it's odd either way.
I'll have to check bitsavers when I get time.
--Chuck
...and others, such as the Siemens FDD-100
(single sided) will
output an "illegal medium" signal if double-sded floppies are
inserted.
Interesting. I think the single-sided drives I've dealt with just
never assert READY, because they don't have a sensor at the index
position of a double-sided medium. 
8:04 p.m.
On 8/12/15 4:21 PM, Chuck Guzis wrote:
I could have that reversed--and that SS media in the
FDD-200 would cause an "illegal media" signal to be asserted, but it's odd
either way.
I'll have to check bitsavers when I get time.
An FD-200 service manual would be nice to have a scan of. I don't have a copy.
It is a little embarrassing that all I have up for Siemens are two floppy disk manuals.
10:15 p.m.
I went back to the FDD-200 manual. The signal is ILLEGAL PACK and is on
the FDD200, not FDD100 --that's logical.
Sorry, I've been distracted by personal events lately.
--Chuck
5:50 p.m.
On 8/12/2015 3:26 PM, Chuck Guzis wrote:
...and others, such as the Siemens FDD-100 (single sided) will output an
"illegal medium" signal if double-sded floppies are inserted.
--Chuck
Hmmm. I have an FDD-100-8 (single sided). The manual mentions no such
signal and only one index sensor/detector, and I don't see it on the
schematic either. Schematic/manual reference? Maybe this was something
on very very late models?
JRJ
10:22 p.m.
Chuck Guzis wrote:
On 08/12/2015 11:12 AM, Jerome H. Fine wrote:
If I remember correctly, the DSD 880/30 provided the DY(X).SYS
device driver in RT-11 with a bit that specified if the index hole was
for a SS or a DS floppy media. If the media was SS, DY(X).SYS
would select ONLY side 1 for any operation. If the media was DS,
then side 2 was also allowed. So the index hole for DS media was
used to determine if sectors on side 2 should be allowed to be read
or written. The signal for DS media did not actually change what
happened except to support (or not support) the use of side 2.
One rather interesting aspect was that the DEC code did not alternate
between side 1 and side 2 as the head advanced. All of side 1 was
processed first followed by all of side 2. As a result, when a floppy
media with a SS index hole was written on both side 1 and side 2, a
DEC RX02 drive could still read all of side 1.
On other hardware which also supported the same electrical and LLF
setup, the DS 8" floppy media device driver alternated between side 1
and side 2. If a floppy media from that system was using in a DEC
RX02, only the first few sectors on side 1 could be successfully
read.
If anyone actually wants to know, I can look up the code. It must
have been more than 15 years ago when the device driver was
enhanced.
Jerome Fine
I forgot to mention one item. Since I had VERY
few Double Sided
media with the index hole offset that extra 1/2" from the Single Sided
index hole - and I have many RX02 compatible floppy media which
are Single Sided with the index hole in the wrong place for being a
Double Sided media - I added a DPDT switch to the sense circuit
of the DSD 880/30 drive. In the normal position, the Single Sided
floppy media are detected as Single Sided floppy media. In the
opposite position, a Single Sided floppy media is detected as Double
Sided and the DSD 880/30 is then able to read / write both sides
of the floppy media. Since the DSD 880/30 is also able to perform
a LLF (Low Level Format), I am able to use all of the RX02 media
as Double Sided WITHOUT the inconvenience of having to punch
the extra index hole.
My drives are configured to take either index signal--so it doesn't
matter if the media is coded as SS or DS. Many floppy drives can do this.
11:08 p.m.
On 08/12/2015 07:22 PM, Jerome H. Fine wrote:
One rather interesting aspect was that the DEC code
did not
alternate between side 1 and side 2 as the head advanced. All of
side 1 was processed first followed by all of side 2. As a result,
when a floppy media with a SS index hole was written on both side 1
and side 2, a DEC RX02 drive could still read all of side 1.
That's not unusual, at least in the CP/M world. A very common ordering
was all of side 1, then side 2, but in descending track order (i.e, from
the innermost to the outermost cylinders). Or side 1, then back to
cylinder 0 on side 2. Some started in the middle of the disk (i.e.
cylinder 37 or so, then writing cylinders 36->0 and then 38->77,
alternating sides--or not.
Wonderful stuff.
--Chuck
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