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The Memotech MTX Series |
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MEMOTECH DISK OPTIONS

This is a work in progress -
to be continued . . . .
SDX Disk Upgrades
As described on the FDX disk option
page, Memotech released a single 5.25" drive upgrade in an FDX
case, which is sometimes referred to as an SDX system, however,
the 5.25" upgrade was not labelled as an SDX. The Memotech
Single Disc Operator's Manual appears to be a compilation of
various other documents and does not present a very clear
picture of the SDX options, but does describe both the Single
Disc FDX type and the two SDX badged products that were released
:-
External Drive SDX
This upgrade allowed the user to install one or two floppy
disk drives alongside the MTX, but with a much reduced footprint
from the FDX option. The disk controller was in an aluminium
case, profiled to match the MTX, which connected to the
expansion connector on the left hand side of the MTX. The
product datasheet for the original SDX disk option notes that
the disk controller is an FDC03, although I am aware that some
external disk SDX systems used an FDC05 controller, but do not
have any information on any differences between the two, or
whether there was an FDC04, or other controller boards used.
The disk
controller was capable of controlling two floppy drives which
could be a mixture of 5.25" and 3.5", although Memotech only
supplied 5.25" disks in this configuration. The floppy drive was
housed in its own case which included the drive's power supply,
a ribbon cable connected the floppy drive to the disk
controller. As the disk controller required more power than the
MTX PSU could provide through 5V line on the expansion
connector, the floppy disk PSU provided an additional 5V supply
to the disk controller via a small power cable between the disk
drive unit and the SDX controller, terminated with a 3.5mm jack
plug at both ends.
Supported Disk Formats
The
SDX FDC03/05 disc controller supported a subset of the config codes
contained in the
PROM of the FDXC1 controller :-

These config codes allowed the use of 100kb, 250kb, 500kb and
1MB (unformatted sizes) floppy disks, the FORMAT program was
capable of formatting up to 8 different configurations, i.e.,
the four sizes on either 5.25" or 3.5" disks.
Expansion Options
Memotech developed a combined 80 Column and RS232 board which
could be attached to the internal edge connector of the MTX,
this allowed the SDX system to be upgraded to CP/M with a
similar package of software as the FDX, including NewWord and
SuperCalc.
There is a copy of the Memotech "Flyer" for the "Memotech
5.25" Disc System" on the Articles
page which includes some technical data on this version of the
SDX,
Internal Drive SDX
For the MTX512S2, Memotech combined the SDX disk controller
and a 3.5" floppy drive into a single unit which connected to
the expansion connector on the left hand side of the MTX. Due to
the extra height of the floppy drive, the profile no longer
matched the contours of the MTX, but it was a much neater
solution. The combined 80 Column and RS232 board was also
installed in the MTX512S2.
The disk controller was combined with a Silicon Disk board,
which allowed a Silicon/RAM disk up to 512kb to be configured.
As the disk drive did not have its own power supply like the
external floppy disks, this controller module also required
external power to be provided to supply the required voltages
for logic circuits and disk drive operation. In this case, the
SDX unit has a 6-pin DIN power connector like the MTX power
input and needed a second MTX power supply unit.
Supported Disk Formats
I believe that the disc controllers in the later
version of the SDX was programmed with config codes "00" to "07"
as per the FDX FDCX1, however, the SDX was hard coded to just
allow types "03" and "07", i.e., DS/DD 40 Track and DS/DD 80
Track respectively.
All 3.5" disks are 80 Track, and apart from the
very earliest, are double-sided and either double (DD) or high
(HD) density. Higher capacity 3.5", HD disks, with a
formatted capacity of 1.44mb were introduced in the late 1980s
and became a standard (defined in ISO9520) in 1989. These disks have an
additional hole in the case, opposite the write protect switch,
to allow the drive to determine the disk density. You can force
a HD disk to be treated as a DD disk in an HD drive by covering the media
density hole with opaque tape.
A comparison of a number of PC formats and the
SDX format is shown in the table below :-
Target hardware |
|
SDX 03 |
SDX 07 |
IBM PC |
IBM PC |
IBM PC |
Disk Size |
inch |
3.5" or
5.25" |
5.25 |
5.25 |
3.5 |
Bytes per Sector |
b/s |
256 |
256 |
512 |
512 |
512 |
Sectors per Track |
spt |
16 |
16 |
8 |
9 |
9 |
Tracks per Side |
tps |
40 |
80 |
40 |
40 |
80 |
Sides |
s |
2 |
2 |
2 |
2 |
2 |
Formatted
capacity =
b/s
* spt * tps * s / 1024 |
kb |
320 |
640 |
320 |
360 |
720 |
A 3.5" drive, with appropriate disk formatting,
should be compatible with Type 03 (40 Track) or Type 07 (80
Track) config modes, but neither of these SDX modes are
supported by the standard DOS or Windows formatting utilities.
However, disks can be formatted for SDX use on a PC using low
level disk tools such as Teledisk 2.15, available on the
Tools page. Version 2.15 is preferred
over 2.16 as it supports Direct I/O whereas 2.16 does not.
VVVVVVV delete VVVVVV
Disk Interface

As described in the Floppy Disk Controller
manual, Memotech managed to use a pin-out that is pretty much exactly
opposite to the original
Shugart interface. The table below provides a
cross reference between the FDX pin-out and the standard used by
just about everyone else
Pin |
Name |
Dir1 |
Description
(Original Shugart Interface) |
FDX J3
Pin |
Modern PC
Interface5 |
Pin |
Description |
--- |
|
|
Head Load (non-Shugart) |
333 |
--- |
|
2 |
/REDWC |
 |
Reduced Write Compensation (8"
only) |
--- |
2 |
Density Select |
4 |
/INU |
 |
In Use (non-Shugart) |
--- |
4 |
(Not used) |
6 |
DS3 |
 |
Device Select 32 |
294 |
6 |
(Not used) |
8 |
/IDX |
 |
Index |
27 |
8 |
(As Shugart) |
10 |
/DS0 |
 |
Device Select 02 |
25 |
10 |
Motor Enable A |
12 |
/DS1 |
 |
Drive Select 12 |
23 |
12 |
Drive Select B |
14 |
/DS2 |
 |
Device Select 22 |
21 |
14 |
Drive Select A |
16 |
/MTRON |
 |
Motor On |
19 |
16 |
Motor Enable B |
18 |
/DIR |
 |
Direction |
17 |
18 |
(As Shugart) |
20 |
/STEP |
 |
Step |
15 |
20 |
(As Shugart) |
22 |
/WDATA |
 |
Write Data |
13 |
22 |
(As Shugart) |
24 |
/WGATE |
 |
Floppy Write Enabled |
11 |
24 |
(As Shugart) |
26 |
/TRK00 |
 |
Track 0 |
9 |
26 |
(As Shugart) |
28 |
/WPT |
 |
Write Protect |
7 |
28 |
(As Shugart) |
30 |
/RDATA |
 |
Read Data |
5 |
30 |
(As Shugart) |
32 |
/SIDE1 |
 |
Head Select |
3 |
32 |
(As Shugart) |
34 |
/RDY |
 |
Ready (non-Shugart) |
--- |
34 |
(As Shugart)6 |
Odd numbered pins are
connected to ground |
|
|
|
Notes : |
1 Direction
indicates that the signal direction is from the
controller to the drive |
2 Legacy drives from different
manufacturers may have ID select numbered 0 to 3 or
1 to 4 |
3 Pin 33 on the FDCX1 board is
only connected to ground, leaving this signal always
ON, see the
FDC schematic |
4 There must be an misprint in
the FDX manual, it should be pin 29, not 28, the
FDC schematic
confirms this |
5 A PC Floppy Disk interface
only supports the use of two drives |
6 I don't think this is
actually used on a PC |
Drive ID Selection
The original design of the floppy disk drive used
jumpers on the drive to set its address which would be
selected by controller pins 6, 10, 12 & 14. Most modern drives,
particularly 3.5" drives for PCs, do not have ID jumpers and are
factory configured to have an ID of 1. (It makes for quicker
assembly when the drives do not need to be individually set up
by the PC manufacturer.)
The table explains how the
twisted floppy cable on a "modern" PC is used to perform drive
selection when only two drives are present, the cable between the first and
second drive connectors has pins 10 to 16 reversed
between the connectors. Both drives should be set to an ID of 1,
the drive connected to the first (untwisted) plug would
therefore be Drive 1 (PC Drive "B") and the drive connected to
the second connector, after the twist, would be Drive 0 (PC
Drive "A"). This picture, from
the PC Guide website
shows a typical Universal (supporting both 3.5" and 5.25"
drives) PC floppy cable - a full explanation can be
found on the PC Guide
Floppy
Interface Cable webpage.
Drive Rotational Speed
The details on drive IDs become particularly relevant if you are looking
for a modern drive to replace an original Qume drive. If that is
the case,
another consideration is the rotational speed of the drive. The
data transfer rate between the drive heads and the host
controller is a function of the media density and the rotational
speed of the drive. For the QumeTrak 142, the rotational speed
is 300RPM and the transfer rate is either 125 kbit/s (single
density) or 250 kbit/s (double density).
The rotational speed of the Qume drive is common
to all legacy 360 kb 5.25" drives as well as all 3.5" drives,
but "modern", HD 1.2MB, 5.25" drives have a rotational speed of
360RPM. This potentially means that an older disk controller
would not be able to handle the higher data rate (500 kbit/s)
from a "modern" drive. Some drives, for example most Teak
drives, have a link selectable speed option for 300 or 360RPM,
most newer 5.25" HD drives do not.
If you want to try modifying a 1.2MB, 360RPM
drive to operate at 300RPM,
this page from Dave Duffield how to do it.
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