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I want to connect 23K256 SPI RAM to ATmega. Do ISP programming will work together with SPI RAM connected.

Thanks.

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  • \$\begingroup\$ always check the available hardware/application notes available from the manufacturer. In this case, Atmel has an app note exactly for this. This question and similar answers have also been asked before. The app note says, place 1K resistors in series between the AVR and the SPI peripheral bus, making sure the ISP connections are BEFORE the series resistor, closest directly to the ATMEGA. \$\endgroup\$
    – KyranF
    Commented Oct 16, 2014 at 16:01
  • \$\begingroup\$ I checked AVR042: "AVR Hardware Design Considerations". But don't see exact resistor value. \$\endgroup\$
    – kesrut
    Commented Oct 16, 2014 at 16:37
  • \$\begingroup\$ the example diagrams and i'm fairly sure the text clearly shows 1k resistors \$\endgroup\$
    – KyranF
    Commented Oct 16, 2014 at 17:57
  • \$\begingroup\$ I apologize, I double checked and cannot find suggestions for actual resistor values. I have seen before that others have used 1K resistors, but I have also seen people use up to 4.7K resistors. If you intend to do fast SPI clock speeds to peripherals use a lower resistor value. Also make sure ALL SPI based peripherals have their chip select pins pulled high with weak (100K will do) resistors to ensure they will not respond to/interact with the SPI bus during programming of the AVR \$\endgroup\$
    – KyranF
    Commented Oct 16, 2014 at 21:00

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From AVR042: "AVR Hardware Design Considerations", section 3.1.1, "Shared use of SPI programming lines":

If additional devices are connected to the ISP lines, the programmer must be protected from any device, other than the AVR, that may try to drive the lines. This is especially important with the SPI bus, as it is similar to the ISP interface. Applying series resistors on the SPI lines, as depicted in Figure 3-2, is the easiest way to achieve this.

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  • \$\begingroup\$ And value of resistors ? \$\endgroup\$
    – kesrut
    Commented Oct 16, 2014 at 16:27

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