If someone wishes to upgrade a PCW8256 by adding a B: drive I would always recommend a 3.5" drive . It is cheaper than a 3" B: drive and the discs are a fraction of the cost. At the time of writing used 3" A: drives are available, but 3" B: drives are becoming harder to find.
Making a basic data cable
To make a basic cable you require one 26-way plug IDC connector, one 34-way socket IDC connector and a length of 26-way IDC ribbon cable. The length of the cable will depend on whether the drive is to be fitted internally or externally. An internal cable need be only 10cm long, connector to connector, an external cable should be around 50cm. long. Making a cable needs some expertise, so if you haven't used this technology before, get some practice first, take loads of time and check as you go or get it made up by someone who's done it before. Components vary, so the following can only be a general guide.
The cable may have multicoloured strands or it may be grey with one outside
coloured strand ; I prefer the latter. It's less confusing and cheaper. The
cable assembly should, by convention, be constructed with the coloured strand
to pin 1 of the 26-way connector as is the existing cable.
Push the 26-way connector on to one of the connectors in the computer. If you're
lucky the new connector may fit the one-way interference lugs. If not they'll
need doctoring. Assemble the cable so that the coloured stripe is in line with
that of the existing cable then crimp securely using a special crimping tool
or failing that a small vice. At the other end slit up a distance of about 8cm.
between the 6th and 7th strands counting from the coloured strand end. Push
the 34-way connector on to the 3.5" drive and feed the cable into it, leaving
about 3cm. protruding. The coloured stripe should be on pin 8 and the other,
plain, side on pin 34; thus there will be a gap in the cable at this end where
pins 14(Drive Select 2) and 15(Ground) are missed out. Crimp at this end.
You should now have a cable which makes the connections as shown in the table below. Check it out. Note that pins 1 to 7 of the 3.5" drive are either not connected or are grounded, so are not used.
| 3" drive pinouts | 3.5" drive pinouts |
| All odd pins are grounded | All odd pins are grounded |
| 1 = Grnd | 7 = Grnd |
| 2 = Index | 8 = Index |
| 3 = Grnd | 9 = Grnd |
| 4 = Drive Select 0 | 10 = Drive Select 0 |
| 5 = Grnd | 11 = Grnd |
| 6 = Drive Select 1 | 12 = Drive Select 1 |
| 7 = Grnd | 15 = Grnd |
| 8 = Motor On | 16 = Motor On |
| 9 = Grnd | 17 = Grnd |
| 10 = Direction | 18 = Direction |
| 11 = Grnd | 19 = Grnd |
| 12 = Step | 20 = Step |
| 13 = Grnd | 21 = Grnd | 14 = Write Data | 22 = Write Data |
| 15 = Grnd | 23 = Grnd |
| 16 = Write Gate | 24 = Write Gate |
| 17 = Grnd | 25 = Grnd |
| 18 = Track 0 | 26 = Track 0 |
| 19 = Grnd | 27 = Grnd |
| 20 = Write Protect | 28 = Write Protect |
| 21 = Grnd | 29 = Grnd |
| 22 = Read Data | 30 = Read Data |
| 23 = Grnd | 31 = Grnd |
| 24 = Side 1 Select | 32 = Side 1 Select |
| 25 = Grnd | 33 = Grnd |
| 26 = Ready | 34 = No Connection |
The Amstrad 3" drive has a Ready signal which appears on pin 26 when the drive is ready to be used. A light in the drive shines through the hole which can be seen near the hub of any 3" disc and as the disc rotates a series of pulses are created which indicate that the disc is rotating at the correct speed. This signal appears on pin 2 and is termed the INDEX signal. A small circuit on the PC board of the drive converts this signal and others to the READY signal which appears on pin 26. In the absence of this signal the computer will not recognise the drive.
Modern 3.5" drives don't use this signal, so an artificial signal has to be produced. You will see from the table above that pin 26 is connected to pin 34 of the 3.5" drive; some suppliers of 3.5" drives for the Amstrad solder a wire between a chip on the PC board of the drive, and pin 34 to create the signal. This is only possible with a few models of drive, is a very skilled operation and a bad procedure can wreck the drive in an instant. Therefore the drive becomes a special and difficult to replace. Another way is to use a small electronic circuit which uses signals on other pins such as INDEX and MOTOR ON to feed into pin 26. This is an excellent solution but I haven't cracked it yet.
My own solution which gives limited success, is to connect the signal from pin 8/16 (MOTOR ON) directly into pin 26/34 as follows. Remember that I asked you to leave 3cm. beyond the 34-way connector? Slit back and isolate the MOTOR ON line and bare the end. Cut through line 26/34 between the connectors and close to the 34-way connector, slit it back a little then connect the wires by soldering. Thus the signal from MOTOR ON appears on pin 26 of the computer, but not on pin 34 of the drive. This is because some 3.5" drives have some sort of signal on pin 34 which may cause interference and malfunction.
This cable works OK with the PCW8256 and PCW8512 in most instances, but there are restrictions. For example, there must be two drives, A: and B: When using Locoscript, there must be discs in both drives or the program hangs. Inserting a disc remedies the situation so I find this no problem. CP/M in general works with no restrictions, except when using DISCKIT. If you remove the discs from the drives when requested, DISCKIT insists that the discs are still in the drive. To get over this problem I put a 5 volt signal on to the same cable joint as mentioned earlier (26/34) via a pushbutton. When told to remove the discs I press the button and any key and DISCKIT responds. The only danger is that by this method the discs can be left in and may be accidentally formatted. However if you don't want to fit the pushbutton, discs can be copied, formatted and verified using Locoscript 2, 3 or 4.
This method cannot be used simply to replace a 3" drive in a PCW9512, as the computer assumes that there is an A: and a B: drive and refuses to function. Adding a 3.5" to the existing 3" drive or adding two 3.5" drives is OK.
What constitutes an A: or a B: drive?
Amstrad 3" drives are hard wired to be either an A: or a B: drive
3.5" drives can usually, although not always, be configured as A: or B: by a
switch or jumper. A switch usually has two positions marked 0 and 1. When on
0 the drive is configured as an A: drive, and vice versa. Similarly jumpers
are often marked D0, D1 etc. The lower position is the A: drive. Look near the
cable connections for the switch or jumper. If there is none, the drive is probably
hardwired as B: In some systems two 3.5" B: drives were employed with a twist
in the data cable between connectors reversing Drive Select 10 and Drive Select
1.
Using the pinout table above other mods. are possible, such as a side switch which switches beween sides of a 3.5" disc to emulate a 3" CF2 disc where the sides are formatted separately to 180K. This is done by switching Side 1 Select(pin 24/32) to ground and back to select one side or the other.
This file has dealt only with the data cable. See also the general file on fitting 3.5" drives.
The diagram below shows how the complete cable with ready signal should look. Length will be to suit the application.
Legend
1 26-way plug IDC connector 2 26-way IDC cable (line points to coloured strand) 3 34-way socket IDC connector 4 Push-to-make pushbutton.The wires should preferably be soldered together and insulated with heat shrink tubing.
Ron King, Andover, England
Email address.... ron@king27.freeserve.co.uk