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[SOLVED] Programmer prior to ISP?

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Newbie level 6
Apr 19, 2015
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Hello! Pretty basic question. Was wondering how microcontrollers were programmed if not through ISP. What actually happens when the microcontroller is taken out from the circuit and programmed by putting it in a socket? Can you point out the details like the protocol used in that method of programming and hardware details?

Both are same. In adapter and also in your circuit the programming lines of the MCU will be connected to ICSP header to which the programmer connects. An adapter can be used to program different MCU like say different PICs but in your dedicated circuit only the MCU of that circuit will be programmed. In your circuit also the programming lines will be connected to ICSP header.
For the device´s point of view, there is no difference between program into the socket or in circuit. The only remark is if circuit must support programing at runtime, I/O uC pins must have at bus pull-up / pull-down components in order to force allowed logic state for these signals during programing.
I would add that ICSP by definition uses a serial method to 'clock' the data into the device. Before this became normal practice, devices were parallel programmed by applying byte sized data across several pins and pulsing a programming voltage of 12.5V, 21V or 25V. The internal program counter would then be advanced to the next address and the procedure repeated with the next data presented in parallel. Most of the devices of that era were OTP (One Time Programmable) in standard packages or they had quartz windows so they could be erased under a UV light source.

That gave much clarity! Thanks! :thumbsup:

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