The TRS-80 Journey Continues

[Fred Cisin]

Double sided drives in 4P shouldn't require anything more than software 
patches, to tell the OS (TRS-DOS, CP/M, etc.) that you have and want to 
use the other side.

The Model 3 and 4 disk controller (did the 4P use the same one??) supports 
double sided and uses pin32 as side select (as deity intended).

Therefore, of course, using a drive that was jumpered for model 1 will 
require removing the pin 32 jumper that model 1 used as DS3.

https://www.retrotechnology.com/herbs_stuff/Model4_35_Drives.pdf
(includes model 3/4 FDC pinout)


This includes the 300RPM jumpering for [SEVERAL VARIANTS OF] 55GFR:
http://www.oldskool.org/disk2fdi/525HDMOD.htm
The links on it to TEAC maanuals seem to no longer be supported by Teac.



To test the suspect drive, you could connect it to a PC; with DS1 jumpered 
(instead of DS0), it should work as a "180K" (single sided "360K").