Hi Wolfgang,

To answer your questions regarding Disk IO board:

IDE:

The IDE portion has three resistors (R1, R2, R3) that are used to pull
up or pull down some signals on IDE bus.

The R1 is for CSEL (cable select) signal. This signal is used to
determine master or slave drive configuration, but only if the drive
is configured for cable select, and your IDE cable supports it (most
40-pin cables don't, most 80-pin cables do). As I understand there is
an error in the schematics, so this signal is pulled up, instead of
being connected to the ground (per standard). But it doesn't really
matter if your drive is not configured for cable select.

The R2 is a pull down DMARQ line, it is required by the standard, but
standard specifies higher value (at least 5.6 kohm), I would say that
10 kohm is a good choice.

The R3 is something strange... it is a pull down on -DMACK line. DMA
is not used by Disk IO board, and standard says that -DMACK line
should remain negated during PIO transfers (that is to be in
"inactive" state, which is "high" in this case). Probably it will work
with some drives anyway, as drives really care about state transitions
and not logical levels. I would agree with Rich, and say that R3
should be connected to Vcc instead of GND.

So I would recommend starting without any resistors, and configuring
your drive as "single" or "master" (not "slave", and not "cable
select"). If it doesn't work reliably, try adding resistors.

Floppy disk controller:

It is OK to mix 3.5" and 5.25" floppy drives. But there are few things
that you should check:
- Termination resistors. 3.5" floppy drives normally have non-
removable 1 kohm terminators. Newer 5.25" (IBM compatible 1.2 MB
drives) also have 1 kohm terminators. Older drives (360KB/720KB)
usually have removable 150 ohm (or sometimes 330 ohm) terminators.
Make sure you have either 1 kohm terminators on all drives, or single
150/330 ohm terminator resistor array installed on the last floppy
drive on the cable.
- IBM vs. Shugart cabling. Disk I/O board provides Shugart 34-pin
connector for floppy drives. It is slightly different from IBM PC
compatible connectors: Shugart connector has only one "MOTOR" line
(pin 16), and 4 "DRIVE SELECT" lines (DS1 - pin 10, DS2 - pin 12, DS3
- pin 14, DS4 - pin 6), while IBM connector has two MOTOR lines
(MOTOR1 - pin 10, and MOTOR2 - pin 16), and two "DRIVE SELECT" lines
(DS1 - pin 14 and DS2 - pin 12).

Shugart standard floppy drives have DS* jumpers that allow assigning
the drive number (they connect one of four DS* lines to actual drive
select on the drive). In IBM PC drives, drive is always selected by
DS2 signal (this is hard-wired in newer 3.5" drives). IBM PC uses a
floppy cable with a "twist" that swaps DS1/DS2 and MOTOR1/MOTOR2
signals, which allows accessing two similarly configured drives.

If you want to use multiple drives with Disk IO board you can either
use a straight cable (without twist) and configure different drive IDs
for each drive, or (if you don't have jumpers on floppy drives) you
can build a custom cable, that will connect each of host's DS* lines
to DS2 line (pin 12) of floppy drives.
If only 3.5" drive doesn't have jumpers, you can simply leave it as
ID=2, and configure other drives to different IDs.

- Motor on - since this line is shared, when one floppy drive is
accessed, all floppy drives will turn on their motors, potentially
generating a voltage spike. Be careful with that, make sure you have
plenty of power to have all floppy drives spinning (to make things
worse, 3.5" drives use 5V for their motors, so they create noise for
logic).

Floppy controller jumpers on Disk I/O board:

The J1 jumper connects interrupt signal from the FDC to the ECB (and
eventually to the CPU). Wayne's BIOS don't use interrupts, so you
don't need to install that jumper (but it still should work with this
jumper installed). Some other BIOSes use interrupt or fast interrupt
modes, that require J1 jumper.

The J2 jumper selects connection for the pin 34 of the floppy drive -
on older drives it was "READY" signal, on newer drives it is usually
"DISK CHANGED" signal. The safe default is to put jumper on pins 3-4
(but not on 1-2 as comment on the schematics says). In unlikely event
that all your drives use pin 34 as "READY" you can put jumper in
position 1-3, connecting READY signal from drives to FDC.

J3 and J4 jumpers are used to configure INT/DMA to WAIT delay (for
virtual DMA operation). As far as I know this is not used by current
BIOSes, you can install them per comments on the schematics. Or it
might be possible to omit these jumpers all together, and also omit
IC17 and U20 (in this case need to make sure that REQD signal is not
floating).


BIOS:

I recommend using Wayne's BIOS, it is very configurable and has very
stable floppy support. It also includes FDTST utility which is
extremely helpful for testing and debugging floppy subsystem. FDTST is
also available separately, so you can use it with any BIOS.

Hope this helps.

Regards,
Sergey

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