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There is no standard for in-system programming protocols for programming [[microcontroller]] devices. Almost all manufacturers of microcontrollers support this feature, but all have implemented their own protocols, which often differ even for different devices from the same manufacturer. Up to 4 pins may be required for implementing a [[JTAG]] standard interface. In general, modern protocols try to keep the number of pins used low, typically to 2 pins. Some ISP interfaces manage to achieve the same with just a single pin. Newer [[ATtiny]] microcontrollers with UPDI can even reuse that programming pin also as a [[general-purpose input/output]].<ref>{{Cite web |title=Unified Program and Debug Interface (UPDI) High-Voltage Activation Information - Developer Help |url=https://developerhelp.microchip.com/xwiki/bin/view/software-tools/programmers-and-debuggers/avr-updi-info/ |archive-url=https://web.archive.org/web/20241007021157/https://developerhelp.microchip.com/xwiki/bin/view/software-tools/programmers-and-debuggers/avr-updi-info/ |archive-date=2024-10-07 |access-date=2024-12-17 |website=developerhelp.microchip.com |quote=Shared UPDI pin. This implementation is generally used on devices with smaller packages. The UPDI pin can be re-configured into a GPIO or /RESET pin. In this case, the UPDI functionality is disabled, and a high-voltage source is required to re-enable it. Examples include tinyAVR 0-series, 1-series, and 2-series devices.}}</ref>
The primary advantage of in-system programming is that it allows manufacturers of electronic devices to integrate programming and testing into a single production phase, and save money,
Microcontrollers are typically soldered directly to a printed circuit board and usually do not have the circuitry or space for a large external programming cable to another computer.
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Microcontrollers that support ISP are usually provided with pins used by the serial communication peripheral to interface with the programmer, a flash/EEPROM memory and the circuitry used to supply the voltage necessary to program the microcontroller. The communication peripheral is in turn connected to a programming peripheral which provides commands to operate on the flash or EEPROM memory.
When designing electronic boards for ISP programming it’s necessary to take into account some guidelines to have a programming phase as reliable as possible. Some microcontrollers with a low number of pins share the programming lines with the I/O lines. This could be a problem if the necessary precautions are not taken into account in the design of the board; the device can suffer the damage of the I/O components during the programming. Moreover, it’s important to connect the ISP lines to [[high impedance]] circuitry both to avoid a damage of the components by the programmer and because the microcontroller often cannot supply enough current to pilot the line. Many microcontrollers need a dedicated RESET line to enter in the
== Industrial application ==
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The second method uses [[test point]]s on the board. These are specific areas placed on the printed board, or [[Printed circuit board|PCB]], that are electrically connected to some of the electronic components on the board. Test points are used to perform functional tests for components mounted on board and, since they are connected directly to some microcontroller pins, they are very effective for ISP. For medium and high production volumes using test points is the best solution since it allows to integrate the programming phase in an assembly line.
In production lines, boards are placed on a bed of nails called [[Test fixture|fixture]]. The latter are integrated, based on the production volumes, in semiautomatic or automatic test systems called [[Automatic test equipment|ATE (automatic test equipment)]]. Fixtures are specifically designed for each board - or at most for few models similar to the board they were designed for – therefore these are interchangeable in the system environment where they are integrated. The test system, once the board and the fixture are placed in position, has a mechanism to put in contact the needles of the fixture with the
== Microchip ICSP ==
For most Microchip microcontrollers, ICSP programming is performed using two pins, clock (PGC) and data (PGD), while a high voltage (12 V) is present on the Vpp/MCLR pin. Low voltage programming (5 V or 3.3 V) dispenses with the high voltage, but reserves exclusive use of an I/O pin.
# Voltage is briefly applied to the MCLR (master clear) pin.
# A 32-bit key sequence is presented on PGD.
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# '''USB cable''' - Small and light weight, has support for voltage source and most computers have extra ports available. The distance between the circuit to be programmed and the computer is limited by the length of USB cable - it must usually be less than 180 cm. This can make programming devices deep in machinery or cabinets a problem.
ICSP programmers have many advantages, with size, computer port availability, and power source being major features. Due to variations in the interconnect scheme and the target circuit surrounding a micro-controller, there is no programmer that works with '''''
PICs are programmed using five signals (a sixth pin 'aux' is provided but not used). The data is transferred using a two-wire synchronous serial scheme, three more wires provide programming and chip power. The clock signal is always controlled by the programmer.
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[[File:pic icsp.jpg|thumb]]
* ''' V<sub>pp</sub>
* ''' V<sub>dd</sub>
* ''' V<sub>ss</sub>
* ''' ICSPCLK
* ''' ICSPDAT
* ''' AUX/PGM
=== RJ11 pinout ===
[[File:Rj11-4-6 to icsp.jpg|thumb|RJ11 to ICSP PIC programmer]]An industry standard for using [[Registered jack#RJ11|RJ11 sockets]] with an ICSP programmer is supported by Microchip.
==References==
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