Re: [CAD_CAM_EDM_DRO] Re: Interface. Gauging interest.

Alan Marconett wrote:

> WHO was doing something with the DLP2232M module? (please contact me) I'd
> like to hear a little more about that. There IS buffering (FIFO). Is there
> an interrupt to clock the data out of the FIFO? Another clock to de-couple
> the output as smooth steps?

That would be me!

Yes, there's buffering, and it seems to work pretty well. I seem to be
getting a reliable rate of one byte sent out every 6.5us, and my PC is
not even breathing hard doing the calculations for the step pulses.

Note: no separate clock is needed to output smooth steps -- what's so
nice about this FIFO mode is that the chip clocks data out every 6.5us
for you. If you don't send it anything, the last value you sent just
sits there. The clock rate I'm using right now is 9600 * 16 (153.6kHz).

That makes for a maximum step rate of 76.8kHz, because you have to send
a zero, then a one, for every step. But, since data is clocked out
every 6.5us, that means that you can place the slower STEP signals with
an accuracy of 6.5us (the full resolutions you'd expect with a 153.6kHz
clock).

If I remember right, that's almost as fast as the Allegro chip in the
HobbyCNC board can take it.

There is a line available to clock data out of the thing, but I don't
use it -- the FTDI chip just holds on to the last value, until the next
one is ready to be clocked out. If you wanted to clock the data stream
into an external latch, or use that line to interrupt a PIC, you
certainly could.

In fact, DLPDesign makes such a FTDI+PIC thing, that works exactly like
that. DLP-2232PB has the FTDI chip, plus a PIC 16F277A. Because of the
PIC, it costs a bit more ($50 vs $35).

If I get stuck with the 2232 alone, and the pulse train has problems
coming raw from the 2232 chip, I'll move up to this more expensive
version, and program the PIC to do the pulses for me.

Info is here:
http://www.dlpdesign.com/usb/2232m.shtml

Right now, I run the FTDI chip's output lines directly to a female DB-25
connector, that plugs into a HobbyCNC board, just like a parallel port
cable would. Something like this:

2232's
PortA
0 XStep
1 XDir
2 YStep
3 YDir
4 ZStep
5 ZDir
6 AStep
7 ADir

The FTDI chip also can do simultaneous reads at that same rate (so, as
you're writing bytes, the chip is also reading bytes in at the same time
and sending them back to you), but I'm not doing that sort of thing yet.

Mike