Home/Limit Switch Input through BCD encoder

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08 Nov 2013 01:54 #40642 by k1v1116
Hi
I'm exploring different ways to wire the limit switches on my 3 axis CNC router using the inputs on a standard parallel port.
My machine has hall effect limits on the X and Y and opto interrupts on the Z. All limit switches are N.C (active low) and cannot be wired in series as suggested in most tutorials to conserve input pins.

One of the possibilities is using a 74ls148 (8 to 3 line priority encoder) it will take up to 8 home / limit switches and require only 3 input pins on the parallel port leaving one for the E-Stop.
The question I have is can HAL handle decoding the 3 bit BCD for the limit switches? After reading through the HAL tutorial it looks like I can use basic logic components in HAL to handle this but since this is my first attempt to work with HAL in LinuxCNC I would like some advice / help with this.

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