That darn Intel jingle...
ard at p850ug1.demon.co.uk
Thu Nov 3 12:22:34 CST 2005
> OK, so there goes that irritating Intel jingle on yet another commercial
> for a product featuring one of their chips - thus ensuring that I'll
> make darn sure I shop around for alternatives before ever considering
> one of their chips.
I avoid Intel chips for a much more practical reason -- they often have
some of the most amazing misfeatures you'll ever see....
The worst, by far, has to tbe the 8255 parallel chip. That was clearly
designed by soembody who didn't think what he was doing. For those of you
who've not read the data sheets, any write to the mode control register
clears all output port lines to 0.
Doing anything to the output registers when writing to the mode control
register is bad enough. But setting them to 0 is about the worst thing
that could be done. On reset, all port lines are inputs (sensible, it
avoids a possible contention). Rememebr a TTL input floats high, so TTL
inputs connected to port lines will appear to be logic 1. Then you write
to the mode control register, and all lines you want to be outputs will
be logic 0. Then you write to the ports to set them to the right values.
You have to design a circuit that can cope with the steady 1 after reset
and the 0 after writing to the mode control register.
Sensible poarallel interface chips (Motorola, Rockwell, etc) let you
initialise the output registers and then set the mode/direction. In otehr
words you can keep a port line effecrtively at logic 1 throughout the
But yes, that jingle is so darn annoying...
More information about the cctech