You've got a problem with your micro and you just can't sort
it out on your own? Then write to MIKE COOK. If he can't help
then probably no one can . .
Fitting Wordwise ROM - without 'Bad command'
I WOULD be glad if you could help me as I am having problems
with fitting a Wordwise ROM chip to my upgraded Model A BBC Micro.
I haven't got the full fitting instructions but was told that
I should remove the Basic ROM from position 2 and put it in position
5 and put Wordwise in position 2 as below.
But when I do this it comes up in Wordwise.
It says Old text (Y/N) - put 'N' and get into menu mode.
But then when I type in *BASIC it gives me "Bad command".
I have tried Wordwise in position 5 and Basic in position 2.
but I get a "Bad command" when I try to access Wordwise
with *W.
I have also tried Wordwise in position 2 and Basic in position
3, and the reverse, without success.
I thought that the operating system scanned the paged ROMs from
5 to 2, so the first method I used (with Basic in 5, and Wordwise
in 2) should have come up in Basic.
I would be very pleased if you could explain this to me, as
I have moved the ROMs so many times that I am worried about damaging
them.
I saw Chris Martin's article in your magazine in July 1983 but
found the directions rather confusing. - Penny Holden, Bury
St Edmonds.
• For such a long letter there is fortunately a short reply.
The links S12 and S13 located where the keyboard cable joins
the main printed circuit board have not been snipped.
Thus only one sideways ROM socket can be enabled. Snip these
and it should work.
Interfacing a printer
I have a BBC Model B computer and a Data Dynamics 390 RO (receiver
only) printer. This is a 20mA current loop printer.
The BBC manual states that it is not possible to interface directly
to this type of printer.
Is it possible to buy or make a suitable interface to run it
off the BBC Micro? If so, could you tell me where I might obtain
the appropriate circuitry? - C.M. Ashley, Knutsford, Cheshire.
• The circuitry itself is not much of a problem but a 20mA current
loop supply requires about 180 volts for full spec performance.
You might be able to modify your printer by removing the resistor
in series with the actuator coil.
If you can do this then a simple circuit using a power FET to
switch the current might work.
But you are then faced with the problem of speed. It is more
than likely that your printer works at 110 baud but the BBC Micro
is not designed for these speeds.
Some mods could be done to achieve this speed, but you lose
the use of the cassette system. All in all, probably not worth
the effort.
Altering the volume
A recently purchased BBC Model B (OS 0.1) is causing me a problem
with a difference.
In my case, the sound is extremely loud, especially when used
for games.
Is there any way I can reduce the sound volume short of returning
to the manufacturer? - Edward Martin, Rothesay, Scotland.
• Open the lid of your computer and remove the keyboard. You
should see a small plastic block in the bottom left hand corner
of the main printed circuit board. In there is a screwdriver slot.
This can be used for altering the volume produced by your micro.
On line at a time
THE first computer I used was a Pet. One of its facilities was
TRACE ON and STEP. With this facility I was able to find out what
my program was actually doing rather than what I thought was going
on.
I now have a BBC Model B. Still being unskilled at programing
I find I need the TRACE on. But even when using Ctrl and Shift
I cannot as yet slow down the program to one line at a time.
Can you help by telling me how or if there is a program available
to cope with this problem. - G.K. Gifford, Southampton.
• Use TRACE ON, but before you do, Ctrl-N. This will stop the
screen scrolling and so allow you to see what has happened. However
we think your time would be better spent thinking about what is
happening rather than resorting to the TRACE command.
Checking your DIY
WHEN I bought my machine, a second-hand plain old Model A, I
decided an upgrade was needed.
I sent off my hard earned cash for a complete DIY "A to
B" kit.
This duly arrived, and with my trusty soldering iron I upgraded
it.
Once switched on the micro displayed the required "32k"
and all software worked perfectly.
However as I did the upgrade myself, and as I don't own a printer,
etc., I cannot be sure if all my soldering on the RGB, analogue,
user port and so on was successful, and that's where you come
in, I hope.
Are there any programs, instructions or details available that
I can key in to check these additions?
I hope that you can sort this problem out and that the solution
may also be of use to other readers. - Allan Dunn, Glasgow.
• THERE is no way of testing these additions until you come
to use them. This is because there is no feedback from the end
of the connector back into the computer.
It's just like posting a letter — you have no idea if it has
arrived until you receive some feedback.
Call for the TV man
I HAVE a BBC Model B and was interested in your reply in the
January edition to a reader who was having problems with drifting
patterns across the screen — especially evident when large areas
of a single colour are used.
I get similar effects when running the Acornsoft Snooker game.
The green table is continually traversed by wavy lines, giving
a dirty picture.
You suggest altering the trimmer near the colour burst crystal.
I have assumed that this trimmer is the small circular component
about a quarter inch diameter in the centre of which is a slotted
screw.
Nearby are components marked 17.7345 mHz and R131.
I have tried altering the setting of the trimmer by 180 degrees
in both directions, but it seems to have no effect.
Finally I returned the trimmer to its original setting.
Can you offer any further advice please? - K. W. Biggs, High
Wycombe.
• To get the colour information onto a TV signal — as opposed
to an RGB monitor — it must be modulated.
This is done at about 4MHz and this carrier frequency is introduced
onto the colour signal.
At the TV end there is a notch fiter to take out this frequency.
If it is not removed you will get the colour patterning you complained
of.
This could be due to either bad adjustment or poor design of
your TV. The adjustment is quite easy to make. The only snag is
finding the colour subcarrier trap as it is called.
The best bet is to call in a TV engineer and get him to adjust
it while displaying a computer signal.
If the adjustments have no effect then it is the design of the
TV set that is at fault and I am afraid there is not much that
can be done.
The problem is that colour TV sets were never designed to be
used with computers and as such are not tested on them.
This problem could just be one of component tolerance and it
is likely that an identical set would give much better results.
Planetoid explained
I HAVE a slight problem concerning the loading of one of my
programs on the BBC.
The game is Planetoid by Acornsoft, and when I try to load it
it always gives a "Searching" message at the value of
20, during planet 2.
It then shows value 21 and 22, with its hexadecimal value, and
continues until it shows V2.0. 00 0000.
I will be most grateful if you could give me an explanation
of the matter. - D. Smith, London.
• This one is simple - your tape is faulty.
There is probably a bit of damage on the tape or a spike has
been recorded on it by accident.
Alternatively the tape could have been damaged by a magnet coming
into close contact with the cassette.
In any event if you take it back to the dealer you bought it
from he should replace it.
Blue block mystery
AFTER reading your reply to a letter in the October issue of
The Micro User (page 113), I opened up my BBC Model B to turn
down the volume.
On the left hand side just above the user-defined keys, I found
a blue plastic block and used a screwdriver to turn the screw
inside. This had no effect on the volume.
Underneath the keys, however, was an off-white block containing
a black screw. This turned the volume down.
Can you tell me what the blue block does and how to tell it
is correctly adjusted, since I have altered it by turning the
screw? - N. Spooner, Rye, East Sussex.
• Yes, the colour of the volume control does vary depending
on where the computer was made. What you altered first was the
clock frequency control of the speech synthesiser.
If the synthesiser is fitted you will find that the pitch of
the voice has altered, possibly giving a Donald Duck effect.
As you probably have not got a synthesiser fitted you don't
have to worry. This control needs to be set up for each chip,
so has not been preset.
Full details of how to adjust this are given in the speech synthesiser
user manual.
Why do they do it?
IT'S come to my notice that more software firms are stopping
and starting the cassette motor while loading.
I generally leave my remote jack out to prevent this happening.
At first I thought that it was switching on and off so fast
that the motor wasn't actually stopping, but now I have my doubts.
I am sure that the software firms would realise that the motor
could burn out with this constant stop-start command and so maybe
it's okay, but I would like your opinion.
Why do they do it? Is it another method of preventing copies?
- B.E. Pritchard, Madeley, Salop.
• I am not sure what you mean. The cassette relay is quickly
pulsed at the end of each block but this is done by the operating
system and not the software.
Normally the cassette motor will not stop, as the pulsing is
so rapid.
I cannot think of any way of protecting software by rapidly
switching this relay on and off.
Three (or four) cheers for Mike!
I WOULD like to say how I enjoy The Micro User especially Mike
Cook's articles for which I give three cheers.
I would make it four if I could make his ideas work.
For instance, the relay will switch a sewing machine on or off
but not control it.
I was hoping to stitch 1in or 1cm long from the keyboard, or
with the light pen. - M. Hardy, Tyne and Wear.
• With respect it was not my idea to control a sewing machine.
A computer can turn things on or off quite easily.
Now assuming that you have connected the control to the switch
that turns on the sewing machine motor you can turn it on, and
then after a fixed time turn it off again.
The motor should have then done a certain length of stitching.
You can then calibrate the length of time the motor is on with
the length of stitching required.
This is not usually satisfactory as the length of stitch depends
on a lot of other factors. What you really need is some form of
feedback sensor that would report back to the computer how much
stitching has been done.
This is what I call a non-trivial task. It can be done, however,
and I am sure you will learn a lot in the process.
When you succeed you have the material for a very good article.
I do hope you will give us first refusal on it.
