Re: Black box ??

Hello Jon...

I have corresponded off list with you several times over the last
couple of weeks re: pico system controller. I will be at NAMES on
Sunday to see you demo your boards. If all goes well I would like to
take a set home (quad encoder with diff. input; DAC16; Dig. I/O, and
m/b) to connect to my servo dynamics drivers (sd4-1525).

Did I understand the earlier discussion to indicate that there would
be an EMC BDI install free-for-all at NAMES on Sunday? Would you have more
info on that?

Thanx...Richard in Michigan.

>
> > Hi,
> >
> > The "black box" project is what a number of people on this group
> > (myself included) have taken on independently to get around the
> > bottle-neck of having a PC generate step pulses for CNC motor

drives.

> >
> > Step pulse timing (frequency generation) is a task that places an
> > inordinate burden on the PC. The general consensus is this task
> > should be off-loaded onto external, dedicated hardware.
> >
> > This hardware (the black box) would generate the requisite
> > frequencies (step rates), freeing the PC to do more intelligent

tasks

> > rather than being tied down with this donkey work.
> >
> > Once that had been resolved, the question became how much should

the

> > black box do? Should it just generate frequencies on command from

the

> > PC
>
> If this is all you want to do, then I've already done it! I have 4

encoder

> counters, 4 digital rate generators specifically designed for step

pulse

> generation, plug 16 opto-isolated digital inputs and positions for

up to

> 8 solid state relays, all on one board. This is essentially

implemented

> on one chip, a Xilinx FPGA. (There is one crystal oscillator to

stabilize

> step rates, one chip to drive some LEDs and properly reset the chip

on

> power up, and a one-shot to create a watchdog timer.)
>
> This board connects to the PC's parallel port, and uses the IEEE

1284

> protocol to keep CPU-controller transfers fast.
>
> It can be used either open loop, by counting its own step pulses, or
> closed loop, with encoders on the motors or XY table.
>
> Step frequencies up to 300,000 steps/second can be generated, or
> as slow as one every 1.5 seconds. Step timing resolution of 100 nS
> is maintained at all speeds. Step pulse width and setup and hold
> times between step and direction signals can be programmed by
> software. Each timing can be set from 100 nS to 25.5 uS.
>
> > or should it include the motion routines themselves? If so should
> > it include a display and a keyboard as well?
> >
> > If you are of an ironic frame of mind, you would appreciate the

full

> > circle back to a PC that extension took. That was fine though, it
> > explored fully what role the proposed project should fulfill.
> >
> > There are other parallel efforts that I am aware of, but the
> > conclusion I have arrived at is it will require the use of a
> > microcomputer no matter what the level of "smart or dumb" the box
> > takes.
>
> No, I have PROVED that this is NOT TRUE! There is NO CPU of any
> sort in my design. The bus protocol for IEEE 1284 (EPP printer

port)

> is pretty simple but robust and VERY low overhead. PC motherboards
> permit a byte to be transferred either way with only one CPU

instruction.

> I DEFY anyone to get 100 nS pulse resolution on 4 axes with any CPU
> less than a "Cray on a chip".
>
> > Once that is recognized, it becomes a matter of communications
> > bandwidth that determines the level of "smarts" the box must

contain.

> > Concurrent with that is the requirement that it also provide the
> > maximum flexibility and value for the price (read cheap).
>
> Using a 333 MHz Pentium II and EMC to control my board, the
> control loop reads the current position, updates the net step rates
> and writes them out to the rate generators in 50 uS. With this

CPU, it

> would be practical to run the loop at 10 KHz.
>
> You could run it on a 100 Mhz Pentium classic with a 1 KHz update

rate

> with no problem.
>
> > It will be very interesting what others will come up with. I

belive

> > in the concept enough to have budgeted for a project that will

take a

> > year before it makes a profit.
>
> Two or more of these boards can be connected to the same parallel
> port if more axes are needed.
>
> See http://pico-systems.com/univstep.html for more info on it.
> I will be demonstrating it at the NAMES show April 27-28 in the
> Detroit area.
>
> Jon