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Hardware Latching Encoder Z Index
Posted: Wed Apr 08, 2026 3:52 pm
by TFrenken
Hi Tom,
as far as I know there is no Hardware Latching function in KMotion. With a short Z signal (0.1µm) you have to use quite low speeds when homing the machine. It works ok especially if the slow speed is only used right before the estimated position of the Z signal. However it would be great if Hardware Latching would be possible(Z signal also uses an encoder input).
Regards,
Thomas
Re: Hardware Latching Encoder Z Index
Posted: Fri Apr 10, 2026 10:54 pm
by TomKerekes
Hi Thomas,
Here is a patched Firmware for Version 5.4.1 that adds a latched register for the 24 differential inputs. An FPGA 32-bit register holds the latched inputs in the lower 24 bits. The register is defined as:
Code: Select all
#define LatchedDiffIn 0x1c0 // FPGA Address for 24 Latched Diff Inputs, read as 32-bit word, write 0's to clear
The latched bits will be set on the rising edge of the input. Any pulse greater than 60ns should be reliably detected. Write 0's to bits to clear.
Note it takes several FPGA 16.7MHz clocks to synchronize and set the latches so reading the register immediately (within 120ns) after the rising edge may not yet show the latched status.
Copy these files to the DSP_KOGNA folder and Flash new Version. It will report as Version 5.4.1XXX
DSPKOGNA.bin
DSPKOGNA.out
DSPKOGNA.sym
KMotionDef.h
Here is a test example that assumes Differntial Output #0 has been looped back to Differential Input #0 (CHA0) and pulsed for a fraction of a us to set the bit.
Code: Select all
#include "KMotionDef.h"
int main()
{
FPGA32(LatchedDiffIn) = 0x000000; // Clear all latched bits
printf("%8X\n", FPGA32(LatchedDiffIn)); // display latched bits
// Pulse Differential Output 0 looped back to Diff input 0 for ~ 400ns
SetBit(250);
ClearBit(250);
for (;;)
{
printf("%8X\n", FPGA32(LatchedDiffIn)); // display latched bits
Delay_sec(2);
}
return 0;
}
Re: Hardware Latching Encoder Z Index
Posted: Mon Apr 13, 2026 7:50 pm
by TFrenken
Hi Tom,
as always I am impressed how quick you reply and are able to find a solution. If I understand correctly this latch should make sure the impuls is always detected. However the actual encoder position during the impuls would not be saved in a register. Is it possible to save the encoder counts in an register when an Z signal is detected? If this would be possible this position could be read by a C Program for homing.
Regards,
Thomas
Re: Hardware Latching Encoder Z Index
Posted: Tue Apr 14, 2026 7:04 pm
by TomKerekes
Hi Thomas,
I was thinking moving relatively slow would allow software sampling. Adding hardware capture registers for all the encoders would use significant FPGA resources.
Software encoder sampling at 90us at resolution of 0.1um can be achieved at:
0.1um / 90us = 1.1mm/s
Moving fast at say 100mm/s should locate the Index within
100mm/s x 90us = 9um
So the "slow" scan should only take a fraction of a second.
Re: Hardware Latching Encoder Z Index
Posted: Wed Apr 15, 2026 3:23 pm
by TFrenken
Hi Tom,
thanks again for the quick reply. Of course you are right that with the fast search using the new latching function the slow and precise search would start very near the actual Imdex. Will this latching function be implemented in the new software version?
Re: Hardware Latching Encoder Z Index
Posted: Wed Apr 15, 2026 3:36 pm
by TomKerekes
Yes it should be in 5.4.2 when we release it.