On Sun, 22 Apr 2001 at 18:10:26, you wrote:
(ref: <[EMAIL PROTECTED]>)
>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.
That is very common - called 'common collector'' - sorry about the
unintentional pun. Nasta is the best one to expand on this - to do
with the easiest way to set transistor based output. (less than a page
plse Nasta (8-)# )
My I2C Philips based Parallel interface ( and power driver) input is
just like this - the external world has to pull the line down.
Literally at the last minute, ie between prototype and final board, I
realised that, on my power driver, all outputs would be 1 and enabled at
power up.
I put in a couple of 7804s to invert the 4 L298 power driver enable
lines, and disable output. This causes much head scratching for users,
as the enable lines are inverted logic.
RS232 is similar - but that was based on 'pen down' teletype logic - ie
mechanical. Lau and I kept on getting it wrong during superHermes
design, because the std interface chips invert to 'correct' the data
(8-(#
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