Re: [CAD_CAM_EDM_DRO] Re: Re: Linux EMC RS232?

Ray Henry wrote:

>On Wednesday 05 November 2003 1:54 pm, CAD_CAM_EDM_DRO@yahoogroups.com
>wrote:
>
>
>>Message: 10
>> Date: Tue, 04 Nov 2003 22:22:06 -0800
>> From: Don Rogers <Don@...>
>>Subject: Re: serial vs parallel port
>>
>>
>>
>>>Dear group can EMC use the RS232 port (serial) instead of the printer
>>>port?
>>>
>>>
>>This bring us a question I have had for a few months now. How can you
>>truly synchronize multiple axis when driving them individually via a
>>serial interface, IE from an indexer card vs a step/direction approach
>>from a parallel port. The serial approach indicates giving one axis it
>>instructions and the going to the next axis and giving it it's
>>instructions.
>>
>>

Right! This is a problem. There are several ways to deal with it.

1. Compute the time it takes to send the command to each axis, and include
that time delay in the position interpolation, such that they all stay
aligned
in time by that offset.

2. Have the separate axes all hold the next waypoint until a global execute
command is sent. This special command would be acted on simultaneously
by all axes.

3. Use a communications speed so fast, and a protocol so concise that
the time
offset is negligible.

4. Don't use any protocol at all, just send step and direction bits as
one serial
byte. That byte is received simultaneously by all axes. But, of
course, what
is the point of doing it this way, except to save 7 wires?

>>
>>Having looked at this for a while, I ended up stripping the indexer
>>cards from my drivers to go to a step direction from a single port
>>approach in the hopes that a single Command structure would be better
>>than a discriminate command structure..
>>
>>
>>

Makes sense.

Jon