TRS-80 Gebruikers Vereniging

Actief sinds 1 oktober 1978

View the index hole project - Reading Newdos80 on a IBM-PC 5 1/4" drive

According to the official norm every sector on a floppy has to be surrounded by gaps. These are long rows of FF followed by a list of 00. Most Floppy Disk Controllers (FDC) have their own way to deal with the gap following the index-hole pulse. The TRS-80 FDC handles it easy. A sector may start at the beginning, or even at the middle of the index-hole signal. This is not the case with the PC, their FDC takes account of the gap behind the index hole. That's why a IBM-FDC can only read a sector after the index hole has passed a reasonable time. In other words: After an index-pulse the IBM-FDC needs some time to recover. Newdos chooses to avoid a gap behind the index-pulse and writes the first sector immediately after the index pulse. So, most PC can't read the first sector of a Newdos floppy disc. This is the latest device to intercept the index-hole signal from the (5,25") floppy drive to the floppy disc controller in your PC. In this case it is build and attached to the floppy flat cable where it gets its power from. As you see the device is small enough to fit on your floppy flat cable and doesn't need extern power as (low energy) CMOS components are being use. Installing a small switch will enable your PC to read those nasty Newdos80 floppies or to switch back to (PC) normal operation.

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If you want to build it yourself, here is the electric circuit. Now you can use READDISK (download it from the website of Matthew Reed) or Hypercross. Just put your floppy (Model I NEWDOS80 Double Density) in the 5,25" drive of your PC to create a DSK file for most TRS80 emulators.