26 Feb
2003
26 Feb
'03
10:32 a.m.
From: Patrick Finnegan <pat(a)purdueriots.com>
I recently picked up a TRS-80 model 4, that seems to
have problems with its floppy drives.
<Snipped>
I tried swapping the floppy drives, and that time I
got a "Diskette?" prompt if there was no disk in
the drive, and pressing any keys didn't cause
anything to happen. If I put a disk in the
drive, the machine never displays anything, and
then after 10-20 seconds, the drive light goes out.
I tried connecting only one drive at a time, with
the same results. If I connected a 1.2MB floppy
that I had laying around (a Teac FD-55GFR-149-U),
it did the same thing as if the drives were swapped.
Ok, a quick primer about TRS-80's and Floppy drives:
Unlike IBM Drives, TRS-80 drives are usually hard
jumpered for specific positions (Not always, but
internal drives are..)
What most people in the PC world don't know is that
floppy drives have an addressing scheme similar to
Master/Slave jumpers on hard drives.
They can be set to positions 0, 1 ,2 or 3. And the
last drive in the chain needs to be terminated (like
SCSI Drives).
For external drives, the drives are set to all
selects, and pins are pulled from the drive cable to
determine what position they are in. If you notice on
IBM Floppy drive cables, there is a twist between the
A: and B: connector. That twist brings the select from
the 0 drive to the 1 select pin. All IBM drives are
set to position 1 (second position).
I don't think a 1.2 mb FDD will work properly on a
TRS-80 Model IV for two reasons. The 1.2mb drive is
much more like an 8in drive than a 5.25in drive. And
transfers data at a higher rate.
Unless the drive can autoswitch to the slower 360k
data rate, it won't work on the controller.
And if you did get it to work, it has a different
Tracks per inch capability than 360k / 180k drives.
However, assuming your problem is with the floppy
drives, and not the diskette you are trying to boot...
A 360k XT Style floppy will work fine, and once you
get it booted, a modern OS like Newdos 80, L-DOS,
MultiDos, etc... Will allow you to use both sides of
the drive for 360k storage.
You can even use 720k 3.5 drives in the same way.
I know for the Model I, LNW made a Disk Doubler Board
that worked with 8in drives, and so would accomodate
1.2mb drives. I don't know if such a disk controller
was ever made for the Model IV.
If you have a PC with 360k Drive, you should be able
to run a TRS-80 Emulator and use a disk image of an OS
to make a bootable floppy in 180k or 360k format.
Let me know if I can help you in any way with this.
The Model I/III/IV was my first machine, and I'm
pretty sure I can remember a lot of info regarding it.
And I still have all my books and disks in my closet.
Regards,
Al Hartman
http://www.geocities.com/alhartman
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26 Feb
26 Feb
11:42 a.m.
On Wed, 26 Feb 2003, Al Hartman wrote:
For external drives, the drives are set to all
selects, and pins are pulled from the drive cable to
determine what position they are in.
A minor complication with using DS drives, at least as external, . . .
Didn't Radio Shack used pin 32 for drive select 3?
Isn't that "side select"?
I don't think a 1.2 mb FDD will work properly on
a
TRS-80 Model IV for two reasons. The 1.2mb drive is
much more like an 8in drive than a 5.25in drive. And
transfers data at a higher rate.
Unless the drive can autoswitch to the slower 360k
data rate, it won't work on the controller.
The TRS-80 1,3,4 support a 125K bits per second data transfer rate for the
FM single density model 1 diskettes
The IBM PC,XT,AT and TRS-80 3,4, and "doubler" boards for model 1 (such as
"Percom Doubler") support a 250K bits per second data transfer rate.
The IBM AT supports a 500K bits per second data transfer rate for 1.2M and
1.4M.
The IBM AT supports a 300K bits per second data transfer rate for 360K
disks in 1.2M drives (spinning at 360 RPM.
Weltec made a "special" 5.25" drive that spun at 180RPM, so that a PC or
XT could do 1.2M with a 250K bits per second data transfer rate. (NOT
RELIABLE)
IFF the drive will switch to 300 RPM, (instead of 360RPM in 1.2M mode),
then it might be possible to use it as a "regular" TRS-80 drive, or as an
80 track drive.
If you want to use the 1.2M drive for 1.2M, then you MUST have a 500K bits
per second data transfer rate, which you will not find on any disk
controllers for the TRS-80 other than the ones intended for 8" drives.
(or that ridiculous Weltec drive)
I know for the Model I, LNW made a Disk Doubler Board
that worked with 8in drives, and so would accomodate
1.2mb drives. I don't know if such a disk controller
was ever made for the Model IV.
yes
I think that Micro Mainframes? made a bourd that could do external 8"
drives with a 3 or 4.
The Model I/III/IV was my first machine, and I'm
pretty sure I can remember a lot of info regarding it.
And I still have all my books and disks in my closet.
I didn't have a big enough closet :-(
So all that I have left of my TRS-80 collection is a few books.
--
Fred Cisin cisin(a)xenosoft.com
XenoSoft http://www.xenosoft.com
27 Feb
27 Feb
10:23 a.m.
On Wed, 26 Feb 2003, Al Hartman wrote:
Yes, but the internal and external drive cables are electically totally
seprate, and the select lines for external drives appear on the DS0 and
DS1 pins of the external connector (only). That's why if you manage to
fit 4 half-height drives inside the M4, you have to run a cable to the
external connector on the FDC board also. There is no problem in having 4
DS drives on a M3 or M4
With the Model 1, all drives are external, and there's only one drive
connector. You're then limited to 3 drives if you have any DS ones.
-tony
For external drives, the drives are set to all
selects, and pins are pulled from the drive cable to
determine what position they are in.
A minor complication with using DS drives, at least as external, . . .
Didn't Radio Shack used pin 32 for drive select 3?
Isn't that "side select"?
10:20 a.m.
Unlike IBM Drives, TRS-80 drives are usually hard
jumpered for specific positions (Not always, but
internal drives are..)
Not so. Most genuine Radio Shack drives had _all_ the drice select
jumpers fitted. The edge connectors on the cable had contacts removed so
that only the 'right' drive select signal went to each drive. This
applies to both internal and external drives.
One problem with this is that the side select contact was removed also.
People who fitted DS drives had to make up their own cable (and it was a
lot easier to make a cable with all the contacts in place and to remove
the incorrect jumpers from each drive).
They can be set to positions 0, 1 ,2 or 3. And the
last drive in the chain needs to be terminated (like
SCSI Drives).
This is something that worried me when he started swapping drives around.
If you don't have the termination resistor in place, it won't work, and
may even corrupt the disk (don't ask how I found that out...)
For external drives, the drives are set to all
selects, and pins are pulled from the drive cable to
determine what position they are in. If you notice on
IBM Floppy drive cables, there is a twist between the
A: and B: connector. That twist brings the select from
the 0 drive to the 1 select pin. All IBM drives are
set to position 1 (second position).
The 'IBM twist' also allows for sepearate motor-on signals to the 2
drives, so that the motors can be controlled separately. A total of 7
wires are involved in the twist, but 3 of them are ground.
-tony
7920
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7921
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alhartman＠yahoo.com -
ard＠p850ug1.demon.co.uk -
cisin＠xenosoft.com -
eric＠brouhaha.com