On Mon, Aug 26, 2002 at 10:07:36AM -0700, Barry Gershenfeld wrote:
> >Thanks for all the contributions you gave to my ideas.
> >I will try to follow the idea of use a PIC to do the job.
> >My second choice is to use a Parallel to serial conversor.
> >Rodrigo Real
>
> Note to all: He has a piece of lab equipment that outputs parallel
> data.  End of story.  No pdf readers running on his voltmeter, etc.

I do think that some missed that. However the parallel to serial converter
suggestion was valid. It would convert the parallel output into a standard
RS232 bit stream that could be input into any ordinary serial port.

>
> 1. You tried to read the data by polling the strobe bit.  Yes,
> it is too fast to "catch".

That seems right.

>
> 2. Whatever you used to catch the data (a PC?) may have a feature that
> lets you program the input strobe bit to "latch", rather than
> trying catch it as a transparent read.  You could also
> use interrupts but I'll bet you want to avoid that, for simplicity.

Starting here is where the ACK and BUSY flags of the parallel port can
be your friends as it'll allow for flow control.

> 3. You could use a PIC, but you actually have to solve the same
> problem.  You must either "latch" that strobe input, or make it
> interrupt the PIC.

One other option though: 40 pin PICS have Parallel Slave Port hardware which
creates an 8 bit hardware parallel interface. Not sure about handshaking off
the top of my head though. But in any case the hardware will track the the
strobe so that you don't have to do it in software.

>
> 4. The simplest solution is a piece of hardware on the
> strobe line to either stretch the pulse or latch the data
> entirely, as Peter described.  It would take one chip.

My favority for this is a 74HCT573 or 74HCT574. They will latch all 8 bits.
Add a flip-flop for ACK/BUSY and you're in business because the hardware will
then be completely self latching at whatever speed you want to pull data off.

>
> 5. Note that if you build a serial converter you will _still_
> have to solve the "short strobe" problem.  And once you do,
> converting it to serial really isn't necessary.

Yes if you build one. However if you buy one, it'll have the handshaking built
in.

BAJ

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