RE: All Lights On/All Units Off and Modifying an MT10

["K. C. Li" <li@xxxxxxx>]

On Sun, 11 Nov 2001, Mark Hetherington wrote:

> Not completely no. I am no expert but never claimed to be. How my
mention of
> what binary pattern is sent over the power line is any indication of
either
> my knowledge of the protocol or electronics I fail to see. The pattern
for

Please don't take it the wrong way. The comment wasn't meant to be an
attack on you. It was merely my assumption from what I have read.

> All Lights off is 1101, the pattern for All units off is 0001 so
whether it
> is hardwired or software controlled, this pattern is the required
change.

As my assumption above implied, they are incorrect. The correct 4-bit
binary pattern for All-Lights-Off is 0110 and All-Units-Off is 0000.

> So the button is hardwired to generate the signal? In which case it is
a
> resoldering rather than a reprogramming job? Or the button is wired to
a pin
> which only issues that command? In my original email I did say I had
no idea

No, neither. The buttons are connected to the microcontroller's input pins
in a multi-line matrix arrangement. Using a keypad scanning routine, the
exact button presses may be detected and act upon accordingly. The fact
is, no matter what you do to the buttons or their wiring, you can't
change what the microcontroller has been programmed to send out.

> of the internal workings of the MT10 hence my question. You then
brought up
> the PIC which I further discussed and now I am "obviously
unfamiliar with"
> both electronics and the protocol.

I was only stating my opinion with the information available. If you are
offended by what appears to be a fair assessment, I apologise.

> Without access to other resources I would agree. Reading the firmware
is not
> a problem I expected to face since I have yet to see one where my
contacts
> have not been able to get me the firmware off it. I would be surprised
if

May I ask how many different protected chips your contacts have
successfully cracked? Without access to sophisticated equipment, it is
highly unlikely that your contacts can be as successful as you claimed.

Some factory programmed chips are impossible to read the firmware off them
as the read functions are unimplemented. In fact, I know of at least one
way to make most of the popular microcontrollers firmware impossible to be
dumped out unless one pops the epoxy off the chip body and scan the
EEPROM/Flash area with a scanning electron microscope. Due to the expense
involved, it is usually cheaper to pay someone to write the software.

> the MT10 firmware was that well protected anyway since there can
hardly be
> anything worth the additional expense of protection within it. But
people do

The protection is standard on practically all programmable
microcontrollers. The majority of the protection fuses, when properly
applied, would present a formidable challenge to any would-be cracker.
This is especially so with OTP (one-time programmable) chips.

> go to great efforts to protect the strangest things so maybe the MT10
is so
> highly protected it was impossible. But then again, wasn't that part
of my
> question.

And I believe I have answered your questions.

Regards,

Kwong Li
li@xxxxxxx
Laser Business Systems Ltd.
http://www.laser.com


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