Hi, This is also posted on the forum at: https://forum.linuxcnc.org/27-driver-boards/48217-mesa-7c81-questions#264314 I wasn't sure where the best place to ask these questions was.
I'm converting my new PM-728VT mill to CNC. I have a background in Integrated Circuits and software, but zero machining knowledge. So Linux and FPGA's make more sense to me than all the machining acronyms. I opted to go with a Raspberry Pi 4B / Mesa 7C81 setup because I've messed with Raspberry Pi's a bit, figured it would let me get away with running the UI on an older laptop, and the 7C81 was one of the few Mesa cards in stock these days (LOL). The OS has not yet been installed on the Rpi, nor has any bit file been installed on the 7C81. I would like to have all of the electronics figured out, and a complete plan for the software installation before I do anything. Kudos to the people who wrote the LinuxCNC 2.8 documentation. It's very good, and if I knew anything about machining I'd probably be off and running. I'd like the LinuxCNC software/hardware setup to support: - Limit and home switches on all 3 axes. - CNC spindle speed and direction control to coordinate feed and speed during milling. - A spindle speed encoder to coordinate low speed spindle operation and Z axis feed for threading operations. - A fourth axis for "A" rotation (Future addition). - Automatic flood or mist coolant control (Future addition). I'm looking at all the pin files for the 7C81 and I have some question regarding the modules: PLL - I assume a digital phase locked loop. I assume this is used internally in the FPGA for circuit timing and I don't need to concern myself with it. WatchDog - Timeout circuit. Sounds like this is used to ensure LinuxCNC and the FPGA card haven't lost contact. IOPort - Is my understanding correct that any pin not defined can be programmed as a general purpose I/O? Are these what I connect the limit and home switches to? QCount - I looked at the VHDL code an it looks like this is a timer for something. SSerial - The LinuxCNC documentation says this is for connecting to a MESA smart serial daughter card. So I assume I won't use it. StepGen - Step and direction generation for the various axes. All of the pin files are showing only step and direction pins. The Mesa HostMot2 Driver Section in LinuxCNC documentation under 13.1 actually lists seven possible pins. I'm using ClearPath-SD servos which have Step, Direction, Enable, and HLFB (High-Level Feedback). Attached is a screenshot of what HLFB can be used for. So I'm going to need to figure out how to access more than just step and direction. PWM - Pulse Width Modulation. I have a KBSI-240D signal isolation board and understand how to connect that into my spindle control. But I guess I need two additional boards. A PWM DAC that outputs 0-10v. (There seem to be two basic cards from China under many names available in several places.) Also need a relay board. I was thinking about this one. LED - I guess for LED's but not sure of the specifics. I don't think I need to care. ENCODER - This is listed in the Mesa HostMot2 Driver Section in LinuxCNC documentation under 15, but is not listed as available in any of the 7C81 pin files. That seems like a problem for me since I would like to connect an encoder to the spindle. I know this is a lot of direct and implied questions, and I really do appreciate any help. I'm trying to understand this in depth so I can proceed logically. Thanks & Best Gene
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