This data refers only to the FD-55GFR-149U. There is also a -140 which looks the same and has the same layout. Perhaps it is basically the same drive and this data applies to that one as well. D0, D1, D2, D3 These give the drive address in a daisy chain configuration. U0, U1 Used to select turn-on condition of front bezel light (see below). IU Jumper to make the signal interface terminal 4 be used for the IN-USE input signal. When strap is removed, the input circuit is open and the IN-USE signal ineffective. ML Selects spindle action according to host command. When open, spindle rotates only by MOTOR ON input signal. When jumper is ON motor rotates when (a) MOTOR ON input signal is TRUE (b) front bezel indicator turns on. RY/DC Used to select function of READY/DISK CHANGE signal on terminal 34. When RY jumper ON signal on terminal 34 functions as ready signal, and it functions as DISK CHANGE signal when the DC jumper is ON. LG Used to select meaning of HIGH/NORMAL DENSITY input signal. When on, LOW level of HIGH/NORMAL DENSITY signals high density mode. When off, LOW level of HIGH/NORMAL DENSITY signal designates normal density mode. I and IS Used to select speed of drive. I strap on: dual speed mode designated. (360 rpm High Density, 300 rpm Low Density). Ready state reset once synchronising with a level change of the HIGH/NORMAL DENSITY signal. Both I and IS OFF, single speed mode designated. Speed is 360 rpm regardless of HIGH/NORMAL DENSITY signal. Both I and IS on, dual speed mode is activated but FDD remains in ready state, regardless of level change of HIGH/NORMAL DENSITY signal. E2 Selects output condition of INDEX and READ DATA pulses.When OFF pulses are ouput as in (DIAGRAM NOT SUPPLIED). When ON, output conditions changed to logical expression as follows: INDEX: Index hole detection * DRIVE SELECT * Ready state READ DATA: Read data detection * DRIVE SELECT * Ready State --------------------- * Write operation FG Connects FDD frame to DC 0V. Front Bezel Indicator Selection Jumper Combo. Indicator turn-on condition 1 * * * Drive select 2 IU * U1 Drive select + in-use 3 IU U0 * In use 4 * U0 U1 Drive select + ready 5 IU U0 U1 In use + (drive select * ready) Notes Selection 1 Indicator tuns on when DRIVE SELECT signal TRUE 2 Indicator turns on while DRIVE SELECT signal is TRUE or IN USE signal TRUE 3 Indicator on while IN USE signal TRUE 4 Indicator on when DRIVE SELECT signal TRUE and FDD in ready state. 5 Indicator turns on, on conditions 3 or 4 I do not what the default settings are meant to be. Mine are FG, D1and DC jumpered. On the 3COM web site they make a technical note about these drives (in document 0000526B) and say D0, I, RY and D3 should be jumpered. (No, I don't know the significance of jumpering *2* drive address selections. It does not seem logical.)