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Long SPI bus lines - should I use series resistors?
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Renate:
On a more basic level:
This is a closed source piece of equipment that is putting out 10kbps SPI to a character LCD?
Presumably the character LCD is a stock parallel one with an SPI "backpack"?

If you are displaying additional info, why wouldn't you use a bigger/different/OLED display?
Why not take the 10kbps SPI in and spit out parallel directly to the LCD.
For OLED, you'd be using a separate SPI bus.

What is this "additional high speed data source"?
Why wouldn't this use a separate SPI into your micro?

SPI is really the least shareable bus thing around.
profdc9:
Probably overkill, but I have used ribbon cables alternative every other line as a ground line.  The impedance of this transmission line is about 100 ohms or so.  It also helps to shield noise.  Source termination is not a bad idea either if you use a controlled impedance line.  I have used SPI ribbon cable buses up to 2 meters long and 8 MHz clocking frequency. 
MagicSmoker:
If the SPI bus is multi-drop then I prefer to use split termination at the very end: 220R for each resistor usually works well enough for both traces and ribbon cable conductors. I also use the "assign every other wire as ground" trick with ribbon cables like profdc9 mentioned to good effect in extremely high noise environments like motor drives, plasma power supplies and other unfriendly environments.

T3sl4co1l:
Back in the day, you'd use a TTL bus driver IC at the source end, and an asymmetrical terminator at the far end, 390R pullup and 150R pulldown I believe was very popular.  Spot in the middle of TTL input threshold, a nice match.  Ye Olde ST-412 interface used such a system for the control signals (the high speed data being RS-422). :)

Can do the same today, give or take terminator voltage offset and receiver threshold voltage, with for example 74HC7014 hex precision schmitt buffer.  Very handy device, if a bit obscure.  I mean, all the old bus drivers and receivers are still around, too, if you like. :)

Tim
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