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| How to use a PC 3.5" HD disk drive with your FZ-1 |
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| Recently I bought a used FZ-1 with a dead disk drive.
Fortunately, the disk controller itself was alright - but the drive was
broken. Casio, however, decided to implement the standard Shugart
bus instead of the (nowadays widely used) PC/AT disk bus which - at first
sight - drives a normal PC disk drive useless as replacement part. |
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what the heck.
rainer@buchty.net
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| Floppy mysteries part 1: Japan spins faster... |
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For some kind of reason (there must be one...) the so-called Japanese
3.5" floppies spin with 360rpm like the old 5.25" drives instead of 300rpm
as the rest of the world does.
Unfortunately, almost no floppy I've seen so far has a "speed select" switch
although the commonly used motor controllers have such an input which put me
instantly in hunting mode when opening a TEAC FD-235 (of which I got a few
so an eventually killed drive wouldn't be that big issue here). Having done
so, I played around with a Mitsumi/Newtronics D359. In case you did the
same with other drives, just let me know and I'll include it in the below
table.
| Drive Model | Drive Controller | Modification |
TEAC
FD-235/HF |
BA6478HF
(Rohm) |
Remove W61, attach a switch to W61's pads; solder W61 between
two poles of the switch to allow either W61 to be present (300rpm)
or not (360rpm) |
Mitsumi/Newtronics
D359T3 |
LB1810
(Sanyo) |
see BA6478HF, but use pin 12 of LB1810; notice that 360rpm will
be selected by applying Vcc, 300rpm by GND. |
| generic |
BA6478HF
(Rohm) |
Desolder and isolate pin 3 of controller; attach a switch to pin 3 which
allows pulling that pin to GND (300rpm) or Vcc (360rpm). |
| generic |
BA6492BFS
(Rohm) |
see BA6478HF, but use pin 29 instead of pin 3 |
| generic |
LB1810
(Sanyo) |
see Mitsumi/Newtronics D359/T3 |
Drive modifications for switching between 300 and 360rpm
See here
if and how your disk drive's pin 34 behaviour can be changed from disk
change to disk ready as needed for proper FZ-1 operation.
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| Floppy mysteries part 2: The PC/AT floppy bus |
Let's first have a look at the PC/AT floppy bus (a lot of people, including
me before doing some recherche work, think that it's the original Shugart
bus - this is wrong) bus which is the standard interface for disk drives
since the great success of the PC architecture. It's using a 34pin connector
where all odd-numbered pins are grounded, only even-numbered pins carry
control signals:
|
Pin
|
Direction
|
Name
|
Description
|
| 2 |
out |
/REDWC |
Density Select |
| 4 |
- |
unused
|
|
| 6 |
- |
unused
|
|
| 8 |
in |
/INDEX |
Index Pulse |
| 10 |
out |
/MOTEA |
Motor Enable A |
| 12 |
out |
/DRVSB |
Drive Select B |
| 14 |
out |
/DRVSA |
Drive Select A |
| 16 |
out |
/MOTEB |
Motor Enable B |
| 18 |
out |
/DIR |
Step Direction |
| 20 |
out |
/STEP |
Step Pulse |
| 22 |
out |
/WDATA |
Write Data |
| 24 |
out |
/WGATE |
Write Enable |
| 26 |
in |
/TRK00 |
Track 0 |
| 28 |
in |
/WPT |
Write Protect |
| 30 |
in |
/RDATA |
Read Data |
| 32 |
out |
/SIDE1 |
Head Select |
| 34 |
out |
/DSKCHG |
Disk Change |
PC/AT FDD Connector
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| What's the real standard: The Shugart Bus |
The original Shugart bus doesn't differ much from this layout but enough
to make a standard PC drive pretty unusable together with the FZ-1. But
there's hope, just compare the pinout (again all odd-numbered pins but
without pins 1 and 3 are grounded, for some unknown reason Casio left
these unconnected - grounding them does not cause any harm to drive or
FZ-1):
|
Pin
|
Direction
|
Name
|
Description
|
| 2 |
- |
unused
|
Head Load (not used with the FZ-1) |
| 4 |
out |
/BUSY |
drive lamp lights when low (same as /DS0) |
| 6 |
out |
/DS3 |
Drive Select 3 (tied to Vcc) |
| 8 |
out |
/INDEX |
Index Pulse |
| 10 |
out |
/DS0 |
Drive Select 0 |
| 12 |
out |
/DS1 |
Drive Select 1 (tied to Vcc) |
| 14 |
out |
/DS2 |
Drive Select 2 (tied to Vcc) |
| 16 |
out |
/MOT |
Motor Enable |
| 18 |
out |
/DIR |
Step Direction |
| 20 |
out |
/STEP |
Step Pulse |
| 22 |
out |
/WDATA |
Write Data |
| 24 |
out |
/WGATE |
Write Enable |
| 26 |
in |
/TRK00 |
Track 0 |
| 28 |
in |
/WPT |
Write Protect |
| 30 |
in |
/RDATA |
Read Data |
| 32 |
out |
/SIDE1 |
Head Select |
| 34 |
in |
/READY |
low when FDD is available |
Shugart Bus Connector
|
| Hackware |
| As you can see, only a few lines differ. Casio never planned to use
up to 4 floppies in one system, thus /DS1 to /DS3 are
disabled (tied to Vcc). Only /DS0 is functional and electrically
identical to /BUSY so you can treat this pair as one single signal.
/READY is something unsual to the PC world - according to the
service manual the FDD grounds this signal when all of the following conditions
are satisfied:
-
all the voltages are supplied
-
the floppy disk's rotation is over 84% of the normal rotation speed
-
a floppy disk is loaded
-
/DIR is set to 0
-
head is on track 0 at power on
To make it short: It shows that the drive is accessible. Since the uPD72065
knows about parameters like head (un)load times and seek time, there's
no real need for this signal. However, the FZ-1 does not only need
it but even strictly relys on it (see below).
|
| The interface |
According to the above tables the interface cable allowing to connect
a PC disk drive to your Casio FZ-1 looks like this:
|
Casio FDD Connector
|
PC/AT FDD Connector
|
Description
|
| Pin |
Name |
Pin |
Name |
|
10
|
/DS0 |
14
12 |
/DRVSA
/DRVSB |
Drive 0 Select |
|
16
|
/MOT |
10
16 |
/MOTEA
/MOTEB |
Motor 0 Enable |
|
8
|
/INDEX |
8
|
/INDEX |
Index Pulse |
|
18
|
/DIR |
18
|
/DIR |
Step Direction |
|
20
|
/STEP |
20
|
/STEP |
Stepping Pulse |
|
22
|
/WDATA |
22
|
/WDATA |
Write Data |
|
24
|
/WGATE |
24
|
/WGATE |
Write Gate / Write Enable |
|
26
|
/TRK00 |
26
|
/TRK00 |
Track 0 Signal |
|
28
|
/WPT |
28
|
/WPT |
Write Pulse |
|
30
|
/RDATA |
30
|
/RDATA |
Read Data |
|
32
|
/SIDE1 |
32
|
/SIDE1 |
Side Select (0=Head 1) |
|
odd
|
GND |
odd
|
GND |
Ground |
|
| Casio FDD Connector |
Casio FDD Connector |
Description |
| Pin |
Name |
Pin |
Name |
|
34
|
/READY |
10
|
/DS0 |
Drive Ready / Disk Changed |
Casio to PC/AT FDD Interface Cable
Normally, 3.5" PC drives are jumpered to be drive 1 (that's why they
need that cable crossing). If you don't want to change the drive jumpering,
wire /DS0 and /MOT with their "B" counterparts, otherwise
"A".
What you also need to do, is connecting /READY to /DS0
as shown in the table's second half. Although it might work for other systems,
the FZ-1 doesn't accept the /DSKCHG signal as /READY.
Attention: In my special case using the /MOT
line for motor control resulted in a permanently spinning floppy. This
may result from a defective NAND gate
which drives that line - I just didn't care. Instead of using the /MOT
line I wired /DS0 to /MOTEx which works perfectly for
me.
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| Disadvantages |
The FZ-1 OS unfortunately relys on the /READY signal, which
during normal operation mainly shows the presence of a disk, therefore
it has no error routines dealing with no disk present or a disk being removed
during load/save. When operating with a faked /READY signal such
as shown above the FZ-1 OS doesn't encounter any error - and keeps on performing
the desired disk operation forever. All you can do in this situation is
switching your FZ-1 off and on again...
As long as you take care of your disks being fed into the drive before
performing any disk operation, there's no disadvantage besides the fact
that usual PC disk drives are thinner than the original one resulting in
a small space between drive and drive cover.
See this
website from Frank Durda IV to check if your drive can easily be converted
from disk change to disk ready behaviour on pin 34. |
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