Hello.
I try to reprogram BIOS of ThinkPad X200 notebook "in situ" by OrangePi PC (its SPI bus).
I cannot read it consistently even if on low frequency 32 kHz. I use 100 mm short wires.
On the help page: https://Flashrom.org/Common_problems there is recommendation about matching the impedance of inputs & wires: "The impedances of the wires/traces do not match the impedances of the input pins (of either the circuit/chip on the mainboard or the external programmer). Try using shorter wires, adding small (<100 Ohm) series resistors or parallel capacitors (<20pF) as near as possible to the input pins (this includes also the MISO line which ends near the programmer) and/or ask someone who has experience with high frequency electronics."
I know basic of electrical engineering & a bit about electronic, but I am very very far from expert.
I try to search this mailing list archives for words "capacitor" or "capacitors", but with no demanded answer.
I try google it, e. g. : (ROM|PROM|EPROM|EEPROM)(flashing|program|rewrite)("ISP"|"in situ"|"in system")(capacitor|impedance)"input" -crystal -oscillator but it found me only articles about https://en.Wikipedia.org/wiki/Decoupling_capacitor which I think that I quite understand, yet or documentation from Actel, Advanced Micro Devices, Altera, Atmel, CheckSum, CML Microcircuits, Cypress Semiconductor, Elnec, LAPIS Semiconductor, Lattice Semiconductor, Microchip Technology, Microsemi, Numonyx, Silicon Labs, STMicroelectronics, Texas Instruments, Xilinx etc. sometimes about In-System Programming, but never about these capacitors.
What is better, resistor or capacitor (or combination)? How to connect them? (Resistor is clear - in series with the wire. But what about capacitor? Parallel with which?)
P.S. On page (bottom "Notes about stability") there is recommendation about foiled twisted pair with link to image http://i.Imgur.com/qHGxKpj.jpg - should not be second wire of the pair respectively foil connected to the ground?
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Rudolf Dovičín