# Adding a 3.5 in floppy to the Micromate

A 3.5" floppy - when run in 720k mode - has the same datarate as the 360k 5.25" drive in the Micromate. Thus connecting such a drive should be no problem. However, there are a few snags. One is that IBM screwed up the cable standard with the PC. The other is line termination. Still - no big deal:

- Most 3.5in drives are made for PCs, preset as drive 1 (not zero), and internally terminated with 1k Ohm terminators. Some have jumpers to change the unit# to zero, most do not. If yours does, make sure it is set to 1 (or 2 if counting starts at 1).
- The Micromate uses open collector drivers (74LS06) and 150 Ohm terminators.
- For some situations this difference in termination does not matter. In my case it did, and the solution is to remove the terminator chip from the internal floppy drive. This should work for one or two external 3.5 in drives. Make sure the power supply for the external floppies have common ground with ther system itself.
- The cable-problem is a no-problem for the first 3.5" drive. It is already (or should be) set as drive one, and works right out of the box.
- For testing it is convenient to just ignore the capacity difference between the internal drive and the 3.5in drive. Just format the 3.5in (720k!) floppy using the Micromate format program. It shold work just fine, and you now have a 2nd 400k drive.
- The final step is to make the necessary changes to the BIOS to turn the drive into a 720k unit. You will not be able to format such floppies, but they come preformatted so it should not be a problem. And one of these days, someone will write at format-program for them.  Take a look in the code directory for the BIOS drive table and code changes.
- If you add more drives, you have to make changes to the cable and the drive itself in order to become unit 2 or 3. Please share instructions here if you do this.
