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| SPI trace length |
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| David Hess:
--- Quote from: rstofer on June 19, 2018, 02:57:17 pm ---How fast is fast? I'd hate to think we're talking about 1 MHz and below at 1 foot of trace. --- End quote --- 1 foot is about 1.5 nanoseconds so no problem with most unterminated CMOS. This is the length where fast CMOS starts to have problems which you can see on a fast oscilloscope. --- Quote ---I'm running a 6" cable (unterminated) between an FPGA and an LPC1768 at around 12.5 MHz and there has never been a problem. There are 200 Ohm series resistors on the FPGA board to protect the pins and eliminate reflections. 3.3V logic... --- End quote --- 6 inches is 0.75 nanoseconds so even less of a problem especially with 200 ohm series resistors limiting rise and fall time. |
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