68kMLA Classic Interface

The pinout is compatible with 20 pin ATX. The tower PSU is basically an ATX PSU. The desktop one has the soft power the Mac way instead of the ATX way, so if you want to use a board out of a desktop with ATX you have to swap Jumper J28 over to the other position (it's in the corner near the back of the end PCI slot.

Sounds like a fun little project 😉

Has anyone ever tried to get a PC floppy drive to work with a retail board?

maybe apple was thinking to have a double floppy option and for this added the PC style one but never followed up in SW ?

So I have now, and it doesn't work. No sign of life

Well that’s a bummer! And quick work..

So I have now, and it doesn't work. No sign of life.

Of course I made sure the floppy cable was the right way round and that the drive was plugged into power. I also swapped in a Rev. A ROM and booted Mac OS 8.0 just in case the newer ROM/OS had dropped support for it.

Interestingly theres a short mini-molex cable that hangs off the Beige G3DT PSU that isn't used for anything, but it's the perfect length to reach a PC floppy drive when it's fitted in the floppy bay. I expect it was there just for that.

/** O'Hare/Heathrow specific registers. */
enum {
    MIO_OHARE_ID        = 0x34, // IDs register (MIO_HEAT_ID)
    MIO_OHARE_FEAT_CTRL = 0x38, // feature control register
    MIO_AUX_CTRL        = 0x3C,
};

/** MIO_OHARE_FEAT_CTRL bits. */
enum {
    MIO_OH_FC_IN_USE_LED               = 1 <<  0, // modem serial port in use in Open Firmware
                                                  // controls display sense on Beige G3 desktop
    MIO_OH_FC_NOT_MB_PWR               = 1 <<  1,
    MIO_OH_FC_PCI_MB_EN                = 1 <<  2,
    MIO_OH_FC_IDE_MB_EN                = 1 <<  3,
    MIO_OH_FC_FLOPPY_EN                = 1 <<  4,
    MIO_OH_FC_IDE_INT_EN               = 1 <<  5,
    MIO_OH_FC_NOT_IDE0_RESET           = 1 <<  6,
    MIO_OH_FC_NOT_MB_RESET             = 1 <<  7,
    MIO_OH_FC_IOBUS_EN                 = 1 <<  8,
    MIO_OH_FC_SCC_CELL_EN              = 1 <<  9,
    MIO_OH_FC_SCSI_CELL_EN             = 1 << 10,
    MIO_OH_FC_SWIM_CELL_EN             = 1 << 11,
    MIO_OH_FC_SND_PWR                  = 1 << 12,
    MIO_OH_FC_SND_CLK_EN               = 1 << 13,
    MIO_OH_FC_SCC_A_ENABLE             = 1 << 14,
    MIO_OH_FC_SCC_B_ENABLE             = 1 << 15,
    MIO_OH_FC_NOT_PORT_VIA_DESKTOP_VIA = 1 << 16,
    MIO_OH_FC_NOT_PWM_MON_ID           = 1 << 17,
    MIO_OH_FC_NOT_HOOKPB_MB_CNT        = 1 << 18,
    MIO_OH_FC_NOT_SWIM3_CLONEFLOPPY    = 1 << 19,
    MIO_OH_FC_AUD22RUN                 = 1 << 20,
    MIO_OH_FC_SCSI_LINKMODE            = 1 << 21,
    MIO_OH_FC_ARB_BYPASS               = 1 << 22,
    MIO_OH_FC_NOT_IDE1_RESET           = 1 << 23,
    MIO_OH_FC_SLOW_SCC_PCLK            = 1 << 24,
    MIO_OH_FC_RESET_SCC                = 1 << 25,
    MIO_OH_FC_MFDC_CELL_EN             = 1 << 26, // Heathrow/Paddington only
    MIO_OH_FC_USE_MFDC                 = 1 << 27, // Heathrow/Paddington only
    MIO_OH_FC_ADB_CELL_EN              = 1 << 28, // Heathrow/Paddington only
    MIO_OH_FC_ETH_EN                   = 1 << 29, // Heathrow/Paddington only
    MIO_OH_FC_ETH_XCVR_EN              = 1 << 30, // Heathrow/Paddington only
    MIO_OH_FC_RESET_ETH_CELL           = 1 << 31, // Heathrow/Paddington only
};

unselect-dev

: !unprotected ( val addr -- ) ! ;
: parent >dn.parent @ ;
: delete-node
	>r
	r@
	>dn.peer-nxt
	@
	r@
	=
	if
		0
		r@
		parent
		>dn.child
		!unprotected
	else
		r@
		parent
		>dn.child
		dup
		@
		r@
		=
		if
			r@
			>dn.peer-nxt
			@
			swap
			!unprotected
		else
			drop
		then
		r@
		>dn.peer-nxt
		@
		r@
		>dn.peer-bak
		@
		>dn.peer-nxt
		!unprotected
		r@
		>dn.peer-bak
		@
		r@
		>dn.peer-nxt
		@
		>dn.peer-bak
		!unprotected
	then
	r>
	drop
	;

" /pci/mac-io/swim3" find-package if delete-node then

dev /aliases
" fd" delete-property
" /pci/mac-io/fdc" encode-string " fd" property

dev /pci/mac-io
new-device
" fdc" device-name
" block" device-type
" floppy" aapl,connector
" fdc" compatible
15000 h#100 encode-reg 8100 h#100 encode-reg encode+ "reg" property
13 1 2 aapl,interrupts
-1 0d byte-load-file
finish-device
unselect-dev

" fd" select-dev

dir fd

dev fd
hrfeaturecontrol@ 8 u.r

F3000038 rl@-flip 8 u.r

Manual inject PC style floppy drives support auto mounting inserted disks by monitoring the "disk change" signal. Amigas use it to automount inserted disks.

The schematics show that only drive B is supported - but the twist in my floppy cable sets mine as drive A. I'll try a cable without a twist.

The schematics show that only drive B is supported - but the twist in my floppy cable sets mine as drive A. I'll try a cable without a twist.

now you gotta populate the cache slot and downgrade the cpu

the implementation is probably similar to the one in the lpx-40 reference design.
glad someone is messing with it now, saves me the trouble 😆

now you gotta populate the cache slot and downgrade the cpu

Auto eject is fully supported by the MFM driver when the appropriate jumpers on the LPX-40 logic board are set and an auto-eject MFM floppy drive is installed.

The MFM drive is an industry standard 3.5 inch MFM-only floppy disk drive with the following required features:

■ a Disk In Place output signal on pin 6 (this output signal must be functional when the drive motor is on or off)
■ a Media Density Sense output signal on pin 4 (this output signal is not required to be functional when the drive motor is off, but it must work when the drive motor is on)

The hardware requirements allow the driver to detect the disk presence status and the disk capacity, which reduces the impact of the considerable feature differences between the GCR and MFM floppy drive implementation on the Macintosh.