Re: [CAD_CAM_EDM_DRO] Re: Caliper to PC interface, Part II: Data Format ?????? Help ?

> Yes, but... on the old PS2 parallel ports, the data port could be
> configured for EITHER input or output. On the new PCs, the data port is
> output only. One has to use the status port pins for inputs. The Bi
> directional parallel port was an oddity that is no longer produced, as far
> as I can tell. Maybe
> certain parallel port cards have bi directional ports on them.

Acutally, most modern parallel ports do have bidirectional capability
through one or both of two special modes (ECP and EPP). One mode is
easy to work with, the other is a real bidirectional data bus that can
get a bit more complicated. Anyway, if you do a web search on
'parallel port FAQ', 'ECP FAQ', 'EPP FAQ' I think you will find the
info you need.

There are what makes parallel port disk drives, video capture, network
adapters, etc possible. I know these devices are all going USB, but I
think many computers still support them for legacy reasons.

You might want to use a tristate buffer device so the calipers can
only drive the port once you have configured it in input mode. And
even then, some current limit resistors might be a good idea.

Or if you don't need to read the devices too frequently, simply
multiplexing them may be the best bet. At most you would have to wait
two sample periods to get each sample. I don't know if your software
has the capability to read from three mutualy-asynchronous clocked
serial streams at once anyway?

Chris