MAILBAG
Upgrading a 486
I recently had the experience of
installing AMD 5x86-133 CPUs in
two 486 motherboards, one a Chic
ony brand, the other a Biostar with a
UMC chipset, neither of which was
designed with a 586 CPU in mind.
The AMD 5x86-133 CPU can be made
to work in a motherboard not specifically designed for it by jumpering
it as per an AMD DX4-100 “plus” or
“enhanced” CPU; ie one with power
management functions. Jumpering
it as a plain AMD or Intel DX4-100
will not work. Choose a 3.45V supply
voltage and a 33MHz CPU clock.
At this point the BIOS will identify
the CPU as an AMD DX4 running at
100MHz. For the CPU to run at its
rated 133MHz, a “clock multiplier”
jumper must be set. Look for a jumper
whose function is “jumper open = 3x
clock, jumper closed = 2x clock”. A
Biostar manual describes this jumper
as “DX/DX4 open, DX2 closed”. A
DX4-100 CPU can run (internally)
at either 3x or 2x the motherboard
clock. Normally the bus clock is set
to 33MHz, and the CPU clock = 3x 33
= 99MHz. I suppose one could use a
bus clock of 50MHz and CPU clock
= 2x 50 = 100MHz. I suspect that
the latter combination would result
in faster I/O (eg, faster graphics and
disc I/O) at the same internal CPU
speed. I haven’t tried this, though.
A 5x86-133 CPU uses a clock
multiplier of either 3x or 4x. In this
case, the jumper described above
has a slightly different meaning. An
open jumper selects a 3x clock as
before (99MHz), but a closed jumper
selects a 4x clock (133MHz). This
jumper may take some finding. For
those with a multimeter, one side of
this jumper is connected to earth, the
other to pin R-17 (CLKMUL) of the
CPU. When correctly set, the BIOS
sees the CPU as an AMD DX4 “plus”
running at 4x 33 = 132 MHz. Be sure
to enable write-back mode for the
internal CPU cache (16K).
I wonder if a system using a
clock-doubled 486DX4-100 CPU on a
50MHz bus (assuming this were possible) would be faster than the same
system using a 5x86-133 CPU on a
33MHz bus? What about a 586-133
running at 120MHz in clock tripled
mode on a 40MHz bus?
F. Zabkar,
Barrack Heights, NSW.
Video security sign
has a drawback
I have just read the Video Security
article on page 62 of the September
edition of SILICON CHIP. I feel that
anyone contem
plating using the
sign on page 67 should consider the
following scenario.
Having just burgled your neighbour’s home, burglars about to burgle
yours are confronted by this sign.
Now they must burgle your home
in order to retrieve the tape linking
them with the neighbour’s burglary.
If after ransacking your home they
are unable to locate the tape, their
options are limited, one being to
torch your home in order to destroy
the evidence.
A safer solution for a low security
site such as a home is a sign that
reads: “This property is under VIDEO SURVEILLANCE with Off-Site
Recording”.
Any VCR used for recording
should be well-hidden. If the power
meter box is not secure, then a UPS
(low cost computer type may be
adequate) should be used to power
the VCR, cameras, etc. Although
probably unnecessary for a home
but certainly of value for shop and
business surveillance is a dummy
VCR complete with tape placed in a
prominent position. This tape may
be easily taken by or handed over
(under threat) to a burglar.
K. Forknall,
Northlands, WA.
Backing up
is important
Referring to your editorial in the
July 1997 issue of SILICON CHIP, I
think you hit the nail right on the
head. Many people don’t even think
of or are even told about backups.
This could be due to the view of sales
people assuming that the purchaser
will only use the machine for trivial
or unimport
ant tasks; eg, playing
games.
In many cases the machine will
work OK for a long period of time but
one day it may play up. What’s the
next step? – try to find what’s caused
the corruption and get a backup disc
out and restore the corrupted files.
If you don’t have a backup the data
is unrecoverable and you’ll never
see it again. Even with disc repair
utilities such as Norton’s this will
not guarantee to get any or all of your
data back!
I recently purchased a backup tape
drive for my machine to complement
an already numerous set of backup
floppy discs. Despite this, a couple
of months ago I lost a file due to
corruption and ended up recreating
it from a printout because the corruption had unknowingly been saved
and both machine and floppy had
the corrupted file. You can never be
too cautious!
S. Sidoti,
Lilyfield, NSW.
Burst charging
does the job
I have been evaluating Nicad Battery Charger designs lately with the
intention of building two permanent
installations for domestic use. Two
articles from SILICON CHIP have been
brought to my attention, these being
in the May 1994 and October 1995
issues. Both these featured projects
using the Philips TEA 1100 IC which,
if I have read and understood both
articles correctly, rely on “Delta V”
voltage detection to terminate normal charge mode and progress to
trickle charge.
The reason I mention these two
articles is that I have also read the
excellent article by Horst Reuter from
Smart FastChargers in the January
1996 issue of SILICON CHIP. In his
article he mentions that he is of the
opinion that once the charge voltage
peak is reached and the voltage levels
out, any nicad battery still charging
in the normal charge mode and
which reaches the point where the
voltage starts to drop (the “Delta V”
continued on page 7
November 1997 3
