By John Ilsley for the Master 128 This article explains the difference
between ROM and RAM. How this appears
on a Master. How you have to take the
computer to bits to change between the
two. Then how you can carry out a minor
op on your pride and joy to enable you
to toggle between RAM and ROM with the
flip of a switch instead.
What is RAM and ROM?
There are 4*16k banks of sideways RAM
in your Master 128 this RAM can be used
for programs that you load in from
disc, sound samples for example which
need all the memory they can get. When
you switch the computer off, all the
data is lost and you have to load it
all in from disc again the next time
you want it.
These banks can also be 2*32k ROMS but
not at the same time as being 4 banks
of RAM!.
The ROM sockets are located at the
right hand side of the Master circuit
board. You may plug ROMs into these
sockets. ROMs such as Printmaster or
PASCAL. When you switch the computer
on, the program which is "burnt" onto
the chip is already installed and ready
to run as soon as you issue the correct
* command.
You may put your own programs onto your
own ROM but this needs an EPROM and
EPROM programmer. There have been
advertisements in this mag, people
offering to program EPROMs for you.
There are also two slots at the right
hand side of the Master just above the
numeric keypad. You can plug a
cartridge containing ROMS into these
slots
How does ROM/RAM appear on a Master?
Type *ROMS RETURN
You will see a list of all the standard
ROMs fitted and their ROM slot numbers.
Look at slots 5,6,7 and 8. If there is
a ? next to the number, then this slot
is RAM. If there is the name of a ROM
there, then you have ROM fitted.
If you buy a ROM and want to fit it
into one of the slots on the circuit
board, you have to do 2 things.
1. Take your computer to bits and plug
the ROM into one of the empty sockets.
2. Change a hardware link near the ROM
to tell the computer to recognise the
ROM instead of giving you RAM.
If you then need RAM at a later stage
for playing sound samples for instance,
you must change this link back. There
is no need to actually remove the ROM,
but it still involves removing the
cover of your computer each time you
need to change the link.
There are 2 links. Labelled on the
circuit board as LK18 and LK19. They
are tiny bits of plastic which push
onto two of the three pegs of each
socket. If a link is fitted to the EAST
(the right hand 2 pegs) it tells the
computer to recognise a 32K ROM. If a
link is fitted to the WEST, it tells
the computer to recognise two 16K RAM
slots.
Link 18 is responsible for switching
slots 4 and 5.
Link 19 is responsible for switching
slots 6 and 7.
How can you avoid moving the link?
This project adds a switch onto link 19
so that slots 6 and 7 can be toggled
between ROM and RAM with the flip of a
switch. This can also be carried out
on link 18 in the same manner, instead
of or as well as link 19.
Let's take a look at the inside of a
Master:
West. East.
link 19 ]
slot 6&7
link 18 ]
slot 4&5
Keyboard Speaker
connectors ^ ^ Assembly.
A Minor op on your pride and joy.
Two major points to note: 1. If you are not sure that you can
solder or put a switch in, then don't
try as you may cause serious damage
to yourself and/or the computer.
Instead, take it and these instructions
to a qualified engineer.
2. This project is for the MASTER 128
ONLY! Neither I or 8BIT will accept
responsibility for any damage you may
do to yourself or your computer whilst
following these instructions. I repeat,
if you are not certain of what you are
doing, either ask someone who knows or
quit!
You will need: One miniature SPDT toggle switch.
One piece of insulated wire, about 3ft
in length.
Start by: Cutting the wire into three equal
lengths.
Switch off the computer and remove the
four fixing screws on the underside.
The cover should now lift off.
With the keyboard facing you, remove
the screws that hold the keyboard in
place, unplug the two ribbon connectors
then lift the keyboard out and put it
to one side. You may like to clean the
keyboard now you've removed it.
Lift the speaker case and unplug the
speaker. Put it to one side.
Cap, facemask and rubber gloves. Scalpel in one hand, resus team at the ready. Commence the op! Take each piece of wire and remove 5mm
of the outer insulation from each end.
Put a small amount of solder onto the
end of each wire.
Put a small amount of solder onto each
of the three pins of the switch.
Remove the link from link 19 and put a
small amount of solder onto each of
the three pins of link 19.
Now decide where to mount the switch on
the case. Drill a small hole large
enough to take the threads of the
switch. I have mounted mine on the
bottom right hand corner of the lower
case since this has a large accessible
area capable of taking the switch.
When you have made the hole, take the
switch and the three pieces of wire and
solder one wire to each of the pins on
the switch. As you have already tinned
the parts to be soldered, the rest of
the soldering should be quite simple.
The three remaining wire ends go to
link19. Solder the wire that comes
from the centre pin of the switch to
the centre pin of link19. The other two
wires go to either of the two remaining
pins of link19. Place the wires so they
won't get trapped anywhere be very
careful not to bend the pins together
or to join them with solder.
Carefully put the switch through the
hole and secure it.
Make sure that all your connections are
correct.
Plug the speaker back in. Being careful
to route the wires correctly.
Put the keyboard in place and push in
the keyboard ribbon connectors.
Make sure there are no tools or bits of
solder or wire loose in the computer,
They could cause a short circuit.
Replace the cover.
Power up. You should get the normal
startup sound and message. If you do
not, then switch off immediately and
check all your connections. If you had
no sound, check the speaker connection
very carefully. If you had any other
problems, remove the project from your
machine and contact me!
If the power up was normal, test out
the project by loading files into
sideways RAM banks 6 and 7:
*SRLOAD <filename> 8000 (6 to 7) Q
Then flip the switch and repeat. In
this way you will find out which switch
position gives you 1*64K ROM bank in
slots 6 and 7 with the ROM enabled and
which switch position gives you 2*16K
RAM banks in slots 6 and 7 with
sideways RAM enabled.
You can flip between ROM and RAM at
will. You will find that the RAM images
are still there even after changing
from RAM to ROM and back again.
As I mentioned earlier, this project
was for link 19 only. If you want to do
the same with link 18 the procedure is
exactly the same. You will then be able
to toggle slots 4 and 5 between ROM and
RAM.
I intend to submit more articles like
this in the near future. I have one
planned for the good old BBC B, a
project to freeze the computer.
Has anyone any ideas for a project that
they would like me to attempt on my BBC
or Master?
Happy soldering....!