TRS-80 Model 4 help requested

From: Fred Cisin <>
Date: Thu Feb 27 16:10:00 2003

On Wed, 26 Feb 2003, Tony Duell wrote:
> There is one possible problem with reading M3/M4 disks on a PC. The
> TRS-80s used the Western Digital controller which can read a sector
> closer to the index pulse than the NEC controller used in PCs (this is a
> simplification, but it should do for the moment). Some PC disk
> controllers can't read the first physical sector after the index hole on
> a TRS-80 disk. When I was transferring LSDOS 6.3.1 from disk images on
> the PC to real disks I found I had to format the disks on the PC, not on
> the TRS-80 to avoid this problem.

Another method that often works to work around that problem is to not let
the FDC see the index signal. For drives like the Tandon, a small piece
of opaque tape (write protect tab) covering the hole, or for drives like
the Teac that "need" index to believe that the disk is turning, interrupt
that signal in the cable. But that "bandaid" kludge also means that many
other types of disk errors, such as ERC 4: Sector not found, will be miss
reported by the BIOS as ERC 128: Drive not ready.
Received on Thu Feb 27 2003 - 16:10:00 GMT

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