Re: Confused about synchronous communications


"Tom2000" <abuse@xxxxxxxxxxxxx> wrote in message
news:llt5f3hep1krgnrtf4cu48a2jk01112njo@xxxxxxxxxx
On Thu, 20 Sep 2007 22:28:37 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:

I'm trying to implement a general prarallel port communications program
but
I'm a little confused about the timing issues involved.


Jon,

I'm not sure it's safe to generalize. My advice is to refer to the
data *** for your device of interest and see what the manufacturer
wants and expects.

In general, though, it looks like you have the general principle
down pat.

When I'm bitbanging, I don't try to center the clock, as a rule. I
put my data up, then immediately toggle a clock pulse. Next data bit,
toggle again. Repeat as necessary, as long as that's within the
manufacturer's timing specs.

When I'm reading, I read the data as soon as I detect the
appropriate clock transition.

So far, it's worked.

BTW - when reading, make sure you understand the data ***.
You'll find yourself seeing the first data bit present before the
first clock pulse. If you don't prepare yourself for that conditon,
you'll be chasing your tail.

The data *** is your friend!


Yes, I have been looking at it but was confused because I wasn't sure when
the data had to be rock solid. It showed the data changing but doesn't say
when it has to be ready. I should have known that if its edge triggered then
it should be on an edge. But this is the first time I've done any low level
communications like this and I just wanted to be sure. The data sheets
giving the timing but they assume you already understand the basics.

Just didn't want to assume something that wasn't true and then spend days
trying to figure out why my code isn't working.

I'll go ahead and try to implement the stuff down and see what happens. Just
a slight modification of my code(sending clock 2x as fast).

Thanks,
Jon


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