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.)

Well, there it is folks. I hope after all that typing it is of use to
*someone* and that somebody sticks it in an archive somewhere. Note
that the words are not necessarily exactly as in the data. I have
shortened and reworded the text where possible.

David Maddison