15 Nov
2007
15 Nov
'07
4:44 a.m.
Then they
switched to selling a sandwich board that added a 179x for
double density, while still retaining the 1771, for the oddball DAMs that
it could provide (needed for TRS80)
What was oddball about DRAM (Is that what you meant?)
for those machines?
Well, I'm sure that there ARE some oddball DRAMs, but that ISN'T what I
meant.
DAM is Data Address Mark.
Oversimplifying just enough to offend the experts, . . .
it is a slightly "out of spec" byte (such as missing a clock pulse) that
can be used to provide an out-of-band signal to the disk controller,
to mark the start of a block of data.
The 1771 could provide a bunch of different ones.
The 179x could provide some, but not all of the ones that the 1771 could
handle.
Unfortunately, Model I TRS-DOS (1771) used some that the 179x could not
create. Therefore, there wasn't any practical way to create a disk
using a 179x that UNMODIFIED Model I TRS-DOS could handle.
There are unconfirmed stories that the reason that TRS-DOS used "oddball"
ones was due to a misprint on a spec sheet.
--
Grumpy Ol' Fred cisin at xenosoft.com