Re: A question about parallel port

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Mail List <mlist@t...> wrote:

> Hi all. I joined this group some days ago in order to solve a

problem:

> many (almost all) stepper controllers interface with pc via the

parallel

> port. Usually
> each motor use 2 bits of the LPTx port. To move one motor one must

raise the

> step bit, keep it high for a while and then clearing the bit.
>
> The frequency of this sequence determine the motor speed.
>
> This is not difficult with the outp() functions in W9.x. But what

about

> moving two or more motors at different speeds in the same time ?? I

mean:

> moving motors at speeds that are not multiple of each other. One

have to

> raise differents bits of LPT port and keep them high for different

times.

> Does anybody ever encountered this problem ? I have to drive 4

motors (2

> couples of two motors) and I don't know how to get reliable results.
> Accurate waiting functions in W9.x is a must but this is another

(and very

> difficult) problem.
>
> I'm just wandering how to solve this problem because it's the last

problem

> to solve in order to get my foam cutting machine working.
>
> Thanks anyway for your opinions or suggestions !
>
> Sandro

Well some day it may be possible to have a different timer for
each motor and pulse each one sepatate, currently the number of
times per second a pulse can be send is limited and a individual
pulse for each motor would not allow for any great speed.

The way to do this in a typical cnc situation where several axses
are commanded to a new destination is as follows.
calculate how many steps each axes has to move
example : x1000 y500 z100 steps.
the most number of steps are used to controll the move in this
case 1000 pulses need to be send.
The x axes will be stepping every time,
the y axes will be stepping 500/1000=.5 every 2nd time
and z axes will step 100/1000=.1 every 10th time.

The speed of the move is usually given in inches per minute.
So calculate the combined length of the move in inch and
based on this calculate the time this move should take based
on the feedrate given.
Divide this time by the most number of steps to take in this case
time/1000= time per step.

Depending on the ratio of steps to take the axses receiving only
partial steps may not be perfectly smuth since they need to
skip a step on ocasion.
Linear interpolation is fairly easy when you get to circular
things get more complicated.

Good Luck