In article <[EMAIL PROTECTED]>, Tony Firshman
<[EMAIL PROTECTED]> writes
>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 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-)# )
Yes, agreed, the electronics make it so ...
>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-(#
... you have to keep your wits about you ! ... can be confusing .....
--
Malcolm Cadman
