Second port for limit switches?

If I'm using six axis on the breakout board, do I need a second breakout board for the limit switches or can I use a simple TTL circuit for this?

You can chain them all together in series and just use one input.

If you have managed to connect 6 axes, presumably you need another port anyway for charge pump / enable, coolant relay, spindle relay etc

regards

I read where limit switches are connected in a single loop but felt uncomfortable with that type hook up.
The Linux documentation is some what limited on this subject. Where can I research more on this?

I dont know of any actual docs, it is extremely simple and safe.
One switch breaks, the circuit breaks and everything stops.

It would be very rare that you could not just look at the machine and know immediately which switch had triggered.

Additionally, if you have your soft limits set properly, it should be impossible to hit the physical limit switches unless you lose steps.

I cant remember the last time I actually did that.

regards

As to adding multiple ports. While it may or may not be necessary for your set up. adding and using multiple LPT ports to your pc is not a problem for Linuxcnc. I have a set up that uses a 2 port parallel port PCI card, in addition to the motherboards built in port. While I am not using nearly all of the io on any of the three ports, adding the 3rd port to this machine made connecting it infinitely simpler, since I was adding controls to an existing setup that did not give easy access to the unused io on the 2 LPT ports it was using. And basic breakout boards are cheap.