On Mon, 8 Mar 2021, Ralph Stirling wrote:
Date: Mon, 8 Mar 2021 05:07:15 +0000
From: Ralph Stirling <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: "[email protected]" <[email protected]>
Subject: [Emc-users] Muxed encoder counters vs regular encoder counters
I am making a custom configuration to replace a Fagor 8050
cnc control with Linuxcnc and a Mesa 7i80hd or other triple
2x25 header interface. I have four servo channels, and three
mpg wheels for jogging. There only seems to be four regular
encoder channels, and beyond that muxed counters are required.
I don't see just how the muxed counters work, however. Can
the two types be mixed? I see in various PIN source files a
mux selection pin. How is this used? Here are the relevant
lines from the vhd file:
IOPortTag & x"00" & MuxedQCountTag & MuxedQCountQAPin,
-- I/O 24
IOPortTag & x"00" & MuxedQCountTag & MuxedQCountQBPin,
-- I/O 25
IOPortTag & x"01" & MuxedQCountTag & MuxedQCountQAPin,
-- I/O 26
IOPortTag & x"01" & MuxedQCountTag & MuxedQCountQBPin,
-- I/O 27
IOPortTag & x"02" & MuxedQCountTag & MuxedQCountQAPin,
-- I/O 28
IOPortTag & x"02" & MuxedQCountTag & MuxedQCountQBPin,
-- I/O 29
IOPortTag & x"00" & MuxedQCountSelTag & MuxedQCountSel0Pin,
-- I/O 30
Thanks again,
-- Ralph
You can have as many regular encoders as desired (until 64 or you run out of
FPGA pins)
Muxed encoder save pins by multiplexing the even/odd A,B,Z signals on single
pins, so a FPGA pin A0 caries the A signal for counter 0 when the muxed select
pin is low and the A signal for counter 1 when the select pin is high. Typically
the muxed select pin switches at 6 or 8 MHz so the encoder sample rate is 3 or 4
MHz. Daughterboards with muxed encoders use the output enable lines of the
RS-422 recievers to select whether the even or odd encoder input drives the
FPGA.
Currently you cannot mix muxed and normal encoders in the same configuration (a
driver limitation) but you can use all muxed encoders in a situation where you
have muxed and non-muxed hardware (it just wastes encoders as you get an aliased
encoder with duplicated data when a muxed encoder FPGA pin is used on non-muxed
hardware)
For MPGs I would suggest using the inm module as this provides 4 MPG inputs
that have the 1x mode thats typically desired for MPGs to get one motion
increment per MPG detent (this requires 2.8.1 or >)
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Peter Wallace
Mesa Electronics
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