I'm not sure if these terms are interchangeable or not. What's the difference between ICSP and ISP? Is it simply the reset? I've shown two configurations in this question I just asked. Are they both ICSP?

  • From what I've heard, ISP is the term used by Atmel. ICSP is the term used by PIC.
    – Gerben
    Commented Jan 1, 2016 at 13:41

2 Answers 2


The difference between ISP and ICSP is a hyphen.

ISP stands for In-circuit Serial Programming, and ICSP stands for In Circuit Serial Programming.

Any arrangement that allows you to program a microcontroller while it is in a circuit using a serial protocol can be called ISP or ICSP.

  • 3
    Well, they may the same but, according to Wikipedia, ISP stands for In-system programming Commented Dec 31, 2015 at 22:54
  • 1
    {sarcasm}And of course Wikipedia is always right....!{/sarcasm} At the end of the day they both refer to the same concept using different wording. Semantics are completely irrelevant when they are just an acronym that refers to a concept, the concept being programming a chip while it is in a circuit using a serial protocol.
    – Majenko
    Commented Dec 31, 2015 at 22:57
  • I have also seen sometimes «in situ programming». It's the magic of acronyms, they can tell anything you want 😉
    – AFract
    Commented Mar 31, 2021 at 5:51

According to the Atmega32U4 datasheet:

The device is manufactured using ATMEL’s high-density nonvolatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-chip Boot program running on the AVR core.

I can't find the word "ICSP" in the datasheet. The quoted paragraph doesn't really explain the acronym. It could be an anagram of SPI. ;)

It seems clear to me that "in system" and "in circuit" are referring to the same thing. The program is serial rather than parallel as it uses SPI (Serial Peripheral Interface).

I've shown two configurations in this question I just asked. Are they both ICSP?

Not really two configurations, because the ICSP header on the board is directly connected to the pins you showed in the other configuration. You may as well talk about using different ground pins as a "different configuration".

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