As you might have already read another
user E.Clarke is now to handle
hardware problems, whether or not the
problems will be published as part of
techtips or not is at present
undecided.
As editor of the magazine I personally
think that the Tech Tips logo and style
which spawned the style of the teletext
magazine should be kept, but with a
change of author.
I will of course continue to offer help
to people with software problems or
programming difficulties.
ANDY NIBBS
THE BASDUMP PROGRAM:
What the Basdump program does is copy
any BASIC program currently in memory
up into sideways RAM. It can then be
recalled from sideways RAM.
It can be used to save the BASIC
program being worked on whilst doing
*FORMAT, *COMPACT and other program
deleting star command. Or to keep a
backup in memory of a program which
keeps damaging itself causing a bad
program.
It does not ever load programs off
discs or make programs runnable by
star commands from memory. The article
will tell you how to use it.
I feel sure I have lost some questions
in the time since I last wrote Techtips
If you have a question hardware or
software, don't suffer in silence. Send
you queries to Duncan.
BATTERY BACKUP
S Bodman asked Duncan ages ago whether
or not I could fit a Battery Backup to
a Watford Solderless Rom Board. I have
not got one of these boards so I can
only discuss battery backup in general
in the hope that maybe another members
can put the theory into practice.
Firstly there are two different types
of RAM, Dynamic Ram and Static Ram.
Dynamic RAM chips or DRAMs as they are
commonly known need their contents
to be refreshed continually and any
battery backup for DRAMs would need
to include refresh circuitry. This
would use more power and be more
complex.
The second consideration is how to
actually implement the power changeover
and what backup power source to use.
You can either use a battery and if so
why not use a Nickel Cadmium (NiCd)
rechargable battery and recharge it
when the main power is on. Or you can
use a capacitor.
A capacitor stores electricity and it
is possible to buy capacitors designed
for this purpose. These are available
from Maplin to name but one source.
These generally have values of up to 1F
and are intended for use with low power
CMOS static RAM devices and can suppl
such a device for 1 or 2 weeks. Maplin
stock such capacitors for £4 to £6.
The use of battery backup can be
simplified by using an automatic switch
The ICL7673 Automatic Battery Backup
Switch is designed for battery backup
as the name suggests.
Vo 1 8 Vp
Vs 2 7 NC
NOT S 3 6 NOT P
GND 4 5 NC
The connections 3 and 6 are logic
outputs to switch transistors to switch
high currents. This should not be
necessary for battery backup.
8 1
Vp Vo
+5V
R1 or
ICL7376 batt.
2 volt-
Vs age.
GND
D1
+ 4
Battery
-
Battery backup using rechargeable
battery R1 and D1 perform the
recharging and should be omitted
if the battery is not a NiCd type.
The above circuit either provides +5V
which is normal for computer power
supplies and quite a considerable
number of chips in the beeb need +5V.
If the circuit is not using the main
+5V supply it will provide a 3V or so
from the battery.
Most CMOS static RAMs will hold their
contents at around 2 or 3 volts but
if 3 single cell batteries were used
the 4½V produced should keep CMOS RAMs
happy. The cells used can be AAA types
and as such will not take up a huge
amount of space.
If however, the RAMs are dynamic and
refresh circuitry must be driven you
probably need a +5V supply for both
the circuitry and the RAM itself.
The supply must be close to +5V and
only deviate by plus or minus 5%.
If you do need +5V you might need to
use a voltage regulator. All of these
things shorten battery life.
This is probably my last hardware
scripture the rest is up to Mr E.Clarke
good luck to him.
All the above parts can be obtained
from Maplin. Catalogues are in WHSMITH
shops. The ICL7376 costs £1.48.
ANDY NIBBS