In message <001901c0caae$77bd7880$6d856fd4@o5e1c0>, John Hitchcock
<[EMAIL PROTECTED]> writes
>Malcolm said -
>
>"It also really matters if you get it wrong ( ! ) as a binary 1 sent
>usually does something, and a binary 0 does not."
>
>It certainly does something Malcolm.
>
>I know somebody very well who not so long ago, in a remote process control
>context, put a '1' in a macro when he intended it to be '0'.
>
>The result...?
>
>1. A fire an a treatment oven. (No one was harmed - physically)
>
>2. The first blemish on the factory safety record for >18 months.
>
>3. Negative safety-related £bonus in _all_ factory pay packets.
>
>4. [ ] <- insert your own guess at what might be in the
> personnel file!
>
>5. A sort of absence from the works canteen for a bit!
>
>All for the want of a '0'.
>
>It's (become) a funny old world.
>
>I liked the copper wire bits - still laaaarrfing.
It was confusing with some early control boards, when the electronics
were wired to be active when 'pulled low' to 0; rather than 'taken high'
to 1. Inverse logic.
The convention of 1 = ON ( High ) and 0 = OFF ( low ) does make things
more predictable :-)
A simple robot arm that I helped to build and program used the following
binary commands :-
lower nibble used,
0000 - all OFF - Robot is safe position with nothing happening,
0001 - bit 1 ON ( high ) - gripper closed,
0010 - bit 2 ON ( high ) - lift arm,
0100 - bit 3 ON ( high ) - rotate base turntable.
Thus to pick up and move an object you always need bit 1 ON - 0001. For
the two movements and to keep an object gripped, you need 0111.
Surprising how often students programmed this as 0110 - hence dropping
the object ! An example of the practical effect of getting it wrong.
--
Malcolm Cadman
