ZX Computings - OpenLibra

The @*?$1!&£@
RAM pack
Dear ZX Computing,
I've read many letters which
mirror my own problems with
Sinclair's 16K memory pack.
I bought a 16K RAM pack,
and — like so many
correspondents — have
suffered with bytes of
information altering
themselves before the
computer crashed. When 1
first encountered the problem,
I sent my 16K pack back as I
thought it was faulty. It was
returned with a note to the
effect that there was nothing]
wrong with it.
I have now relieved the
problem of disappearing data
but at the expense of my
ZX80.1 made a number of
'alterations', the first of which
was to abandon the flimsy top
part of the casing. I presumed
that the fault was a heat
problem and hoped this would
cure it. It partly worked and so
I then unbolted the regulator
and heatsink from the board
and left it standing in free air
with an additional heatsink.
This helped greatly, but did
not totally solve the problem.
The final 'modification' was
to remove the casing around
the 16K RAM pack. There are
1 5 chips inside the case which
get quite hot. I now have no
problems with data altering —
except under one condition.
When working on a large
program (3K plus), and
extensively altering the
program, I find there comes a
point where the computer
cannot handle the extreme
alterations.
K Huber,
Hayes End, Middlesex.
* CXPLCMMVr
D A M E I
ZX81
Catty wonder
Dear ZX Computing,
The wonders or u.C's little
machine never ceases to
amaze me. Did you know that
this program actually works:
10 LETC « 1.5
20 LET A - 4.9
30 LET T = 20
40 LET CAT - 49
ZX COMPUTING SUMMER 1962
50 LET CA - 12
60 INPUT X$
70 PRINT VALX$
80 PRINT VAL X$ (TO 2)
Entering either C, CA or CAT
produces the appropriate
answer on line 70, and will
even break down CAT to CA
on line 80 to print 12 as the
answer.
Andrew Field,
Epping, Essex.
And an answer
Dear ZX Computing,
Having read about the various
problems with the 1 6K RAM
pack, I am beginning to
wonder if I am exceptionally
lucky, or are all the other
satisfied ZX80/81 users too
busy writing long and complex
programs to find the time to
write?
I did have some crashes
with the 3K RAM, so I wrote
to Sinclair and received a letter
which included the following;
"We have found that
lubrication on the contacts
soives the problems of RAM
pack connections. You should
first clean the edge connector
with surgical spirit and then
smear it with Vaseline."
I did this and had no further
trouble, and when my 1 6K
RAM arrived I repeated the
treatment. Again, no trouble
at all.
With regard to Sinclair
service, I can only say that I
am very happy. Like many
others, I received a letter
about the 1 6K RAM delivery.
Mine arrived in four weeks. I
had a keyboard fault on the
ZX81 kit that I assembled for
my son. It was replaced by
return post after phoning
Cambridge. We had another
intermittent fault, and as I was
able to go to Cambridge, I took
it to the Sinclair office. I was
directed to the Service
Department where, after
spending some time on it and
failing to find the offending
component, they replaced it
Letters
with an assembled ZX81.
Note that I have no
connection with Sinclair,
except as a satisfied user.
D E F Rolfe,
Haslemere, Surrey.
• PLOSIVE
CAiVUB
- ZX81
Screen invert
Dear ZX Computing,
When writing games for my
ZX81,1 find that I sometimes
need to 'inverse' everything
on the screen at a particular
stage in the program. It is
possible to use a BASIC
subroutine to do this but this
is a slow process — half a
minute or so — so I set about
writing a machine code
routine which could be used in
the SLOW mode.
Type in the following
program:
10 POKE 16388. 0
12 POKE 16389, 127
14 FOR C = 32600 TO 32624
16 INPUT N
18 POKE C, N
20 NEXT C
22 NEW
The numbers to be entered
(line 16) are as follows:
42, 14, 64. 6. 22. 126. 254.
118. 32, 8. 5, 120, 254.0, 32,
5, 24, 6, 198, 128, 119, 35,
24. 237, 201
The routine will still remain at
the top of RAM, even after
NEW, so it can be used for any
program LOADed during a
programming session. You
need to include the following
routine in the BASIC program:
9000 PRINT AT 0,0:
9010 LET RR-USR 32600
Line 90Q0 ensures that the
m/c routine starts scanning at
the beginning of the screen.
The routine takes less than an
eighth of a second to RUN and
is relocatable, that is, it can be
placed anywhere in RAM.
John Miller,
Farlington, Portsmouth.
Och aye the 81
Dear ZX Computing,
Following an advertisement
and a feature in the local
paper, a ZX81 users' club has
been formed in tnverclyde
(Gourock, Greenock and Port
Glasgow). The club is meeting
weekly on Wednesdays at
members' homes in turn.
Our numbers are as yet
small, but they are increasing.
We would be grateful if you
could mention us in 'ZX
Computing', The number to
phone for meeting details is
Gourock 39967.
The club secretary (me) and
one of our other members
attended the ZX Microfair.
bringing back the saga of a
day in London neither will
forget. Not that we would
want to. We only hope it will
be possible to arrange
something similar further north
so that all our members can
have the opportunity of seeing
a wide range of both hardware
and software.
Robert Watt,
Gourock, Renfrewshire.
*Eric Deeson, the organiser
of the EZUG (Educational ZX
Users Group) is planning a
microfair in Birmingham in
September. More details on
that in the next issue of ZX
Computing. Jo find out more
about EZUG, send a large,
SAE to EZUG, Highgate
School, Birmingham B12 9DS.
TH