On Sat, 15 Jun 2019, Andrew wrote:
Date: Sat, 15 Jun 2019 10:30:36 +0300
From: Andrew <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Subject: [Emc-users] 7C80
Hi,
Just wondering about 7C80 board, is it going to be available? Any problems
with SPI link stability? I tried 7i90HD with RPi a while back, but gave up
because of connection issues.
Thanks,
Andrew
I've had LinuxCNC running 24/7 on the 7C80+RPI for about 11 months now with no
hardware issues. This is with a 40 pin cable about 2" long between the RPI and
7C80. If you have interface problems. its very likely a SI ( Signal Integrity )
issue with the cabling.
The (7C80,7C81,7I90) SPI interface uses the FPGAs GCLK. This means it can run up
to 50 MHz or so with a fast host, but it does require good signal integrity.
For random/longer cable connections using a async SPI interface in the FPGA that
simulates the synchronous interface would allow better tolerance of SI issues (
by oversampling / filtering the clock and data in signals ) at the cost of
lowering the maximum clock speed to say 8-10 MHz. I have not bothered with this
since it works reliably with short cables (Actually it works with longer cables
if the clock source impedance is correct for proper series termination, I can
drive a 7I90 in SPI mode at 50 MHz send/recv with another FPGA card and a 2 foot
cable)
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Peter Wallace
Mesa Electronics
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