TRS-80 Model 4 help requested

From: Fred Cisin <>
Date: Wed Feb 26 19:42:01 2003

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
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

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.

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            
Received on Wed Feb 26 2003 - 19:42:01 GMT

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