On Mar 13 2005, 22:45, Randy McLaughlin wrote: and authoritative select does [ ... ] actual sure Well, how about document 5fd0050a.pdf from TEAC's website, which is the spec sheet for the FD-55GFR-XXXX range. Page 1 lists the customer-selectable jumpers for -3xxx, -4xxx and -5xxx as including "LG" and "I". Page 7 shows where all the jumpers are. Page 8 lists the jumpers for -7xxx. Page 13 states (the CAPITALS are in the original document) ---------------------------- begin --------------------------------- LG strap: to select the logical meaning of the Hi/Normal DENSITY input signal at interface line #2 LG Strap OFF ON -------------- -------------- ------------- Density mode HIGH LOW HIGH LOW I/F #2 signal HIGH LOW LOW HIGH For an AT compatible system LG should be set to the off state. I Strap: Strap to select the rotational speed mode of the FDD for the Hi and Low density modes. ---------------------------- end --------------------------------- In other words, Pin 2 is the Density Select signal, and can be jumpered to work so that 0V (signal active) sets HD and inactive sets low density (SD/DD, or FM/MFM). Normally it's not fitted, so active (low) sets low density and inactive (or open-circuit) sets high density -- as you woould want for an IBM AT or similar. The "I" jumper controls whether the Density Select signal *also* controls the speed -- a *secondary* function of the Density Select. If fitted, speed changes when density does; if not fitted, speed is fixed at 360 RPM. Pages 16-21 of the same PDF file on TEAC's website are a scanned copy of TEAC's "FD-55-GRF-XXXX Instalation Guide" for use with IBM AT, which clearly shows the factory settings of the jumpers, with neither "LG" nor "I" fitted, so Pin 2 selects density as usual, and the signal on pin 2 does not affect the speed, which is fixed at 360 rpm. If you want more, I have data for Mitsubishi MF504C-310MP, on which jumper SS sets single speed (360 rpm) without affecting density selection, same for Mitsubishi M4854-35, Panasonic JU-475-2.AGG (jumper AX makes density select on pin 2 be latched when drive is selected, BX/CX/JX determine if speed is determined by density select or is fixed, and 1M forces it to ignore the density select signal on pin 2), and Fuji FDD5883AOK (Toshiba) which has a jumper from pin 2 to ground labelled "DD" for double density and described as disabling HD (jumpers DE/DX are described as to set the speed according to the density, or fixed). Think about this: All HD-capable 5.25" drives need a way to set the density (by changing the write current) for either 300 oersted media or 600 oersted media. The drive has no way to tell on its own. Therefore there must be some signal defined to do this. AT controllers can write both densities at 360 rpm (they just use a 300kbps clock instead of a 250kbps clock), so they don't actually need to change the speed. Therefore the signal previously unused (or, rarely, used in non-standard vendor-dependant ways) on pin 2 is the density signal; using it to reduce the speed is an optional extra. Your FD55 happens to have a jumper fitted to make the speed change when you change the density, that's all. -- Pete Peter Turnbull Network Manager University of York