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NEVER1B.TXT
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2006-10-19
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ORIGINALLY PUBLISHED IN LIMA NEWSLETTER MARCH 1990
^^^^^^^^^^^^^^^ LETTER TO THE EDITOR
{Editor's note: The following letter refers to the
article "Never Released Official TI Modules - Part 1" by
Charles Good, published in the Jan 1990 issue of BB&&P.}
Well over five years ago a 99'er in New Jersey, by the
name of Dennis Porpora, noticed the diagnostic grom for sale
in a parts list supplied by TI. It was quite inexpensive so
he bought about ten, and using unwanted game modules, etc.
made up replicas of the TI Diags module. He even published
schematics and instructions which appeared in n/l's from
coast to coast. I believe that grom is still available from
TI.
I am doubtful about your asumption, mentioned in your
article on the disk duplicator module, that "track copiers
were unknown" when it was created. the manual for the
Western Digital #1771 chip (used in the TI disk controller)
gives sufficient information for a track copier to have been
written and it clearly identified both the sector register
as well as the track register and both read sector/write
sector and read track/write track procedures. Incidently,
copies of the Western Digital manuals for the controller
chips 1771, 1772, 1773 (used by TI, CorComp, and MYARC) are
available from Beery Miller of 9460 NEWS.
Programmers, such as Barry Boone, only had to write
Western digital for the manuals to know all the information
that TI was so anxious to conceal and could write track copy
programs. As a matter of fact, several of the so called
"track copiers" actually read 9 sectors rather than 1 track,
but the point is moot since they all work pretty well. In
any event the formatting of disks by DM1 and DM2 is via
track write, de facto evidence TI knew how to handle data by
tracks. Have I sufficiently beaten that point to death?
A track or sector copier could have/should have been
incorporated into DM1, 2, and/or 3. I think TI deliberately
left it out so as to have an additional module to sell at
some future date.
All evidence shows that with the exception of the Mini
Memory and Editor Assembler modules {Editor's note: also the
LOGO and PLATO modules} TI kept all the utility modules as
well as game modules within the limits of the 9918 VDP
chip's RAM so that none required memory expansion. Even so,
with a track taking up only 2304 bytes plus small overhead
for the track header (as opposed to a sector's 256 bytes) a
track copier should have been in the DM modules -in fact
with the 9918's self incrementing RAM, easily done. More
than likely, however, it would have meant an additional GROM
in the module. Most TI modules simply dumped the grom
contents into VDP RAM and were not used thereafter. My
assumption, which you are free to doubt because neither of
us knows for sure what went on in the heads of the TI
programming teams, is that since the DM module was sold (or
given away) with the DC card, TI was being cost conscious.
If the code ran over 8K grom, the second grom would have had
to be bank switched much like the XB module's groms, or if
the combined program and storage space needed for a track
copier exceeded the 16K VDP RAM, the second grom would then
have to be dumped in as a second program by itself,
superseding the first grom. If the extra grom cost TI $5 (a
wild guess), and if TI planned to sell even 25000 of the
double density cards with the DM3 thrown in, you can see the
money involved.
If TI planned to sell the separate Disk Duplicator
module for $50, you can understand why such programs were
not made part of the DM modules.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Arthur J. Byers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Central Westchester 99ers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^1261 Williams Dr.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Shrub Oak NY 10588
.PL 1