Pluto_servo is an emc2 software driver and associated firmware that allow the Pluto-P board to be used to control a servo-based CNC machine. The Pluto-P is an inexpensive ($60) FPGA board featuring the ACEX1K chip from Altera. Pluto_servo is released under the terms of the GNU General Public License version 2. The pluto_servo system is suitable for control of a 4-axis CNC mill with servo motors, a 3-axis mill with PWM spindle control, a lathe with spindle encoder, etc. The large number of inputs allows a full set of limit switches.

The board features:

• 4 quadrature channels with 40MHz sample rate. The counters operate in "4x" mode. The maximum useful quadrature rate is 8191 counts per emc2 servo cycle, or about 8MHz for EMC2's default 1ms servo rate. An axis with index pulse must have fewer than 8192 counts per revolution.

• 4 PWM channels, "up/down" or "pwm+dir" style. 4095 duty cycles from -100% to +100%, including 0%. The PWM period is approximately 19.5kHz (40MHz / 2047). A PDM-like mode is also available.

• 18 digital outputs: 10 dedicated, 8 shared with PWM functions. (Example: A lathe with unidirectional PWM spindle control may use 13 total digital outputs)

• 20 digital inputs: 8 dedicated, 12 shared with Quadrature functions. (Example: A lathe with index pulse only on the spindle may use 13 total digital inputs)

• EPP communication with the PC. The EPP communication typically takes around 100uS on machines tested so far, enabling servo rates above 1kHz.

Pluto-servo is now in the CVS HEAD of emc2. There's documentation and a manual page with all pin names listed.