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XX-01DF4-E1

May 2000

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Document:	RX50 Substitution Application Note
Order Number:	XX-01DF4-E1
Revision:
Pages:	1
Original Filename:	http://web.archive.org/web/20151122034308/http:/www.dunnington.info/public/RQDX/RX50_substitute.pdf

OCR Text

RX50 Floppy Disc Drive
The RX50 floppy drive differs from the SA400 standard in several respects:
1)
The RX50 does not need nor use the InUse / HeadLoad signal on pin 4.
2)
The RX50 will not respond to STEP pulses unless the drive is both selected, and MotorOn is valid; most SA400compatible drives will step (if selected) regardless of MotorOn.
3)
The RX50 is effectively two drives with a common spindle and carriage; thus any head movement on Drive 0 will
also affect Drive 1.
4)
The RX50 Ready signal (pin 34) indicates that the drive has a disk in, the door is closed, and is selected,
regardless of whether the motor is running or not. On an SA400-compatible drive, this signal indicates that the
drive has a disk in, is running at full speed (two consecutive index pulses at the correct time interval), and is
selected. The inherent delay (minimum 200ms) prevents an RQDXn from seeing the drive as being ready.
5)
On the RX50, which is a single-sided device, the SideSelect1 signal is used to disable the Track00 output; the
RQDX series controllers use this as a test to determine that the drive really is an RX50 (and really is present).
The first three points are unimportant when using an SA400 drive on an RQDX controller in place of an RX50, but may
in rare cases be significant if an RX50 is used on other systems. The latter two points must be catered for when using
an SA400-type drive on an RQDXn controller. Ideally, this should include disk-in detection, but a simple derivation of
the drive-select signal has been found to suffice if this is impractical. However, such a "fudge" will cause an RQDXn
controller to think a disk is present even if there is not, and any attempt to access the non-existant disk will generate a
"Disk Fault" or "Drive Fault" type of error instead of a "No Disk" or "Drive Empty" type of error.
A Canon MD220 drive can be modified to behave as an RX50
(actually, half an RX50) by adding a 74LS02 IC with some minor
modifications. The diagram on the right shows the original version of
the original circuit; the diagram below shows the modified version.
The switch allows the drive to be used either as an RX50, or exactly as
it was before.

Trk0 (H)

IC11

4 IC9

J5-26
TRK00

DriveSel (H)
2
1 IC9

Ready (H)

J5-34
READY

N.C.
N.C.

1
2 IC16

N.C.

+5V

1k0

Trk0 (H)

IC11

Trk0(H) taken from IC11-8
SideSel(L) taken from IC06-9
Ready(H) taken from a platedthrough hole under IC12
DiscIn(L) taken from a platedthrough hole by RA2

1k0

2 IC16

5
4 IC9

J5-26
TRK00

J5-32

The DiscIn(L) signal was originally
the DoorClosed(L) signal. The door
microswitch was disconnected, and a
new microswitch fitted beside the
head load solenoid to sense the disk.
The drive design is such that this is
only effective if the door is closed.

SideSel1
DriveSel (H)
2

Ready (H)

1 IC9

J5-34
READY

DiscIn (L)
SA400

RX50

+5V
2k2

2k2

CUT

Where it is not possible to provide a DiscIn
signal, a simpler circuit will be effective, subject
to the note about disk/drive errors mentioned
above. This circuit, using an additional 7438, has
been used with a Mitsubishi 4853.

TRK00

P1-26
TRACK

Trk0 (H)

TRK00

from TP13

SideSel1
from IC D5-1

DriveSel (H)
from IC C6-6

P1-34
READY