spencer@oberon.UUCP (Randy Spencer) (04/02/86)
"zipity do da, zipity ay, my oh my, what a wonderful day!"
A while back someone on another net suggested a way to connect
a 5 and 1/4 inch drive to the Amiga, well a friend picked up on
it and designed a circuit board and built the circuit. When he
was done he had a working 5 1/4 drive for the IBM emulator. Since
I have just ordered PC/ET I asked him if I could have a description
of its construction. When he sent it to me I felt that it would
be something of interest to the net. Here than is "How to build
and IBM drive for the Amiga" schematic and all (hope you can
read it). If you have any questions you may contact him or me,
I will hopefully have built one myself soon.
I would be interested in anyone who is working on building an 880k
amiga compatible 5 1/4 " drive. I do however see more practical
use for the 5 1/4" drive to be IBM compatible. Enjoy!
--------------------------------------------
Connecting a standard 5.25" IBM compatable drive to the Amiga
Parts:
DB25 connector (male, ribbon cable type) with pins 13 and 25 cut off
(the pin numbers given from now on will treat it as a DB23 con-
nector, i.e. 1-12 on the top and 13-23 on the bottom-be careful!)
34 pin edge connector for standard disk drives
25 conductor ribbon cable
12 volt power supply at least 1.5 amps
7805 voltage regulator (TO-220 type) for +5 supply from 12 volts
7474 D flip-flop (Commodore uses LS type, but it doesn't seem to
matter)
7438 open collector quad NAND gate
(5) 1K resistors
An IBM compatable disk drive (I used a Qume QT-142 from JDR
Microdevices, $69.95)
You can get everything but the ICs from Radio Shack.
Procedure:
Attach the ribbon cable to the DB23 connector and cut to length.
Cut cable apart so that wires are about 1-1.5 inches long with
about 1/4 inch of the end stripped. (Remember the two end wires
will be pins 13 and 25 of the DB25 connector, which should not
be used.)
Attach the ribbon cable to the 34 pin edge connector as follows:
DB23 34 edge
2 30 Read Data
3-7 1-33 (odd) Ground
13 32 Select Head 1
14 28 Write Protect
15 26 Track 0
16 24 Write Enable
17 22 Write Data
18 20 Stepper Pulse
19 18 Stepper Direction
22 8 Index
I used a 12V power supply and mounted a 5V regulator on the disk drive
itself for the +5V supply. The other connector on the drive is the
power supply input. If unmarked, you can find which pin(s) is ground
by checking for continuity between the alleged ground pin and pin 7
of a 14 pin TTL chip on the board. Pin 14 of a 14 pin TTL chip is +5,
find the +5 input the same way. The remaining input is +12. The motor,
when turning, draws 1 amp from the +12 supply, and the drive draws
about 0.35 amps from the +5 supply (typical values). Power it any way
you like, but make sure it meets these minimal requirements.
Build the circuit given on the schematic, and attach wires (from
Amiga's DB23 connector) 1,8,10, and 21 as shown on diagram.
The outputs of that circuit go to the Drive Enable and Hub Motor
Drive inputs on the disk drive. On my Qume that was pins 16 and
12, respectively. On other drives the Drive Enable might be 12 or 14,
and the Motor Drive 10 or 16. The correct Motor Drive input is the
one that starts the motor spinning when you ground that pin. You
might have to experiment to find the right Drive Enable. (The drive
light will come on when it is grounded, I think).
Notes:
This drive will work ONLY as a 360K IBM drive. It would work as
a standard Amiga drive it it could step past track 40, but it
can't. Perhaps a quad density (like the Teac FD-55F from JDR)
would work, but I don't know if it would function as a standard
IBM drive in emulator mode.
If you want to hook up another drive, build the identical circuit
but use the SEL2B line instead of the SEL1B line. Commodore
"steps down" drive lines as they go through each drive, i.e.
SEL2B becomes SEL1B and SEL3B becomes SEL2B at the output of the
external drive. So when you make this drive SEL1B, the computer
addresses it as df1: if it is hooked up to the disk port on the
back of the Amiga, and df2: if it is hooked up to the port on the
back of the external drive.
The CHNG line (pin 11) is unused in IBM mode. If you try a quad
density drive and want to use it as a normal Amiga drive, then
hook up a switch to ground (?) this line when a disk is removed.
If the IBM drive is plugged in, the drive's power MUST be on.
If the power is off, the system will not boot because it can't
read any of the drives properly. If the Amiga's up and running
and the drive is turned off, the next time the Amiga tries to
read any disk in any drive it will corrupt that disk (I lost
a couple this way before I realized the problem.) So when you
first test your new drive, set the write protects on your
Kickstart and Workbench disks to prevent damage. After that,
keep the power on or unplug the drive from the Amiga when not
in use.
I lifted the schematic directly from Commodore's 3.5 inch Amiga
drives. I take no credit for it (I'm still not sure what it does)
and I'm not making any money from it, so please don't sue me.
If you have any questions or need help, send mail to me at:
Fred Hamilton
511 Warren St., Apt. 16
Blacksburg, VA 24060
Good Luck!
Schematic:
---------
+++++++++++++++++++++++++ (A)
+ |
Symbols: + | 4
------- resistor: + o---|\ 6
______ + | | |O------
! ! | + o---|/
! chip ! \ + 5
!______! / +
\ + (A)
NAND gate: | + |
+ |
-----|\ + o-----o-----o-----o
| |O---- + | | | |
-----|/ + ____|_____|_____|_____|______
+ ! !
junction no-junction + ! 10 11 12 13 ! 8
+ ! Q !-----
| | + ! !
--o-- --|-- + ! 1/2 7474 _ !
| | + ! Q !-----
+ ! ! 9
+++++++++++++++++++++++++ !_____________________________!
+5v +5v +5v NAND gates are 7438
^ ^ ^ All resistors 1K
| | |
\ \ \ +++++++++++++++++++
1K / (A) 1K / 1K / + From disk drive +
\ ^ \ \ + power supply: +
| | | 1 | + +
| o--------o------|\ 3 | + Pin 14- +5v +
| | | |O--o + Pin 7- GND +
SEL1B(21) >--o-------------|---o--|/ | +++++++++++++++++++
| | 2 |
| o--------|--------------o
+5v | | |
^ | o----o |
| 1 | 3 | | |
\ __________O_______|__ | |
1K / ! CLR \/! | |
\ ! ! | 9 |
| 2 ! ! o---|\ 8 |
MTRXD(8) >--o---! D ! 5 | |O----o |
! Q !------|/ | |
+5v ! ! 10 | |
^ ! 1/2 7474 ! | |
| ! ! | |
\ ! _ ! 6 | |
1K / ! Q !---o | |
\ ! ! | | o---> DRIVE ENABLE
| 4 ! ! | |
DRESB(10) >--o---O PR ! | 12 |
| !___________________! o----|\ 11 |
| | |O---------> HUB MOTOR DRIVE
o--------------------------------|/ |
13 |
|
RDY(1) <-------------------------------------------o
DDRIVE 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
DB25 NC NC NC 22 NC ^ NC ^ 19 18 17 16 15 14 2 13 NC
^ | ^ |
| | | |----Qume hub motor drive
| | |
| | |----maybe drive enable
| |
| |----Qume drive enable
|
|----maybe hub motor drive
---------------------------
Usual disclaimers:
If any member of the net is caught or killed, my university will
disavough (sp?) any knowledge of my actions.
Good luck gang!--
==============================================================================
Randal Spencer - Student DEC Consulting - University of Southern California
(213) 743-5363 UUCP...!{uscvax,sdcrdcf,engvax,scgvaxd,smeagol}!oberon!spencer
Arpa: Spencer@USC-ECL or Spencer@USC-Oberon Bitnet: Spencer@USCVAXQ
Home: 937 N. Beverly Glen Bl. Bel Air California 90077 (213) 470-0428
------------------------------------------------------------------------------dvgarlan@uok.UUCP (04/08/86)
Schematic:
---------
+++++++++++++++++++++++++ (A)
+ |
Symbols: + | 4
------- resistor: + o---|\ 6
______ + | | |O------
! ! | + o---|/
! chip ! \ + 5
!______! / +
\ + (A)
NAND gate: | + |
+ |
-----|\ + o-----o-----o-----o
| |O---- + | | | |
-----|/ + ____|_____|_____|_____|______
+ ! !
junction no-junction + ! 10 11 12 13 ! 8
+ ! Q !-----
| | + ! !
--o-- --|-- + ! 1/2 7474 _ !
| | + ! Q !-----
+ ! ! 9
+++++++++++++++++++++++++ !_____________________________!
+5v +5v +5v NAND gates are 7438
^ ^ ^ All resistors 1K
| | |
\ \ \ +++++++++++++++++++
1K / (A) 1K / 1K / + From disk drive +
\ ^ \ \ + power supply: +
| | | 1 | + +
| o--------o------|\ 3 | + Pin 14- +5v +
| | | |O--o + Pin 7- GND +
SEL1B(21) >--o-------------|---o--|/ | +++++++++++++++++++
| | 2 |
| o--------|--------------o
+5v | | |
^ | o----o |
| 1 | 3 | | |
\ __________O_______|__ | |
1K / ! CLR \/! | |
\ ! ! | 9 |
| 2 ! ! o---|\ 8 |
MTRXD(8) >--o---! D ! 5 | |O----o |
! Q !------|/ | |
+5v ! ! 10 | |
^ ! 1/2 7474 ! | |
| ! ! | |
\ ! _ ! 6 | |
1K / ! Q !---o | |
\ ! ! | | o---> DRIVE ENABLE
| 4 ! ! | |
DRESB(10) >--o---O PR ! | 12 |
| !___________________! o----|\ 11 |
| | |O---------> HUB MOTOR DRIVE
o--------------------------------|/ |
13 |
|
RDY(1) <-------------------------------------------o
WHERE IS (A)----- COMING FROM???