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Besides fast general-purpose I/O pins, hardware requirements for running
machctld are minimal.
A good platform for this application is the Soekris
net4801
(266Mhz 586-class CPU, 128MB RAM with 12 GPIO pins), or the
net5501,
with flash or hard drive sufficient to store the largest CNC programs.
Since our CNC programs execute with interrupts disabled, they cannot
be stopped or modified by software-only means during execution. Therefore,
it is essential that all machining equipment include at least an emergency
stop button and limit switches, connected directly to the controller system.
Support for controls requiring more complex electronics, such as manual
pulse generators (MPGs), rotary encoders, feedrate override controls,
LEDs and LCD displays is provided through the cncpanel device.
With our system, these devices interface with a low-cost microcontroller
and interact with the control system over a three wire serial link
(schematics are going to be made available with the 1.0 release).
To avoid disturbing the timing of
motion control signals, a data frame is read from, and written to the
device, at every cycle. The only requirement of the cncpanel device
is the availability to transfer the data frame quickly and at consistent
speed.
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