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| SPI trace length |
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| rakeshm55:
Hi, Is there a limit for trace length for SPI (Single ended) thumb rule ?? My requirement is to take it off-board ie from Module ---> Motherboard---->Module I have referred to following article www.ti.com/lit/an/slla142/slla142.pdf It suggest (<30cm) for single ended trace length for high speed operation. As a thumb rule At what trace lenths should i used differential drivers (LVDS,RS485) etc for SPI interface |
| ataradov:
I had a board with 1 master and 8 slaves with the board length about 30 cm and slaves attached to the bus along the length. It worked at 12 MHz, but was unstable at 16 MHz. The bus capacitance was too high for the MCU pins to drive it. A stronger single-ended driver might have worked better. |
| rakeshm55:
My understanding is that SPI is used for commnication within a Board (Controller to Controller). When taken off-Board say to read a remote ADC wont there be a design guideline suggesting approximate trace length supported for single ended transmission.Or is it just governed by the drive strength and capacitance of the trace. |
| ataradov:
Just the drive strength and capacitance. At some point setup times are not met since it takes time to charge the capacitance of the trace. You can take care of some of that with proper bus termination and all that stuff. At some point you need to consider your bus to be a transmission line and apply the rules accordingly. And I suspect that in my case it would work fine at 16 MHz if it was not for a Christmas tree-like placement of the slaves on the bus. |
| rakeshm55:
So what will be worst case capacitance for per unit length of PCB trace?? |
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