In-system programming: Difference between revisions

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Typically, chips supporting ISP have internal circuitry to generate any necessary programming voltage from the system's normal supply voltage, and communicate with the programmer via a serial protocol. Most programmable logic devices use a variant of the [[JTAG]] protocol for ISP, in order to facilitate easier integration with automated testing procedures. Other devices usually use proprietary protocols or protocols defined by older standards. In systems complex enough to require moderately large [[glue logic]], designers may implement a JTAG-controlled programming subsystem for non-JTAG devices such as [[flash memory]] and microcontrollers, allowing the entire programming and test procedure to be accomplished under the control of a single protocol.
 
== Devices supporting Inin-Systemsystem Programmingprogramming ==
A number of devices presently support in-system programming. These include:
* ARM processors.
* AVR Microcontrollersmicrocontrollers
* PIC Microcontrollersmicrocontrollers
* 8051 based Microcontrollersmicrocontrollers
 
Example of devices using ISP is the [[Atmel AVR|AVR]] line of micro-controllers by [[Atmel]] such as the [[ATmega#Basic families|ATmega]] series.
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[[File:Icsp-pinouts.png|thumb|Typical chip connections]]
 
* ''' V<sub>pp</sub> ''' - Programming mode voltage. This must be connected to the MCLR pin, or the V<sub>pp</sub> pin of the optional ICSP port available on some large-pincount PICs. To put the PIC into programming mode, this line must be in a specified range that varies from PIC to PIC. For 5{{Nbsp}}V PICs, this is always some amount above V<sub>dd</sub>, and can be as high as 13.5{{Nbsp}} V. The 3.3{{Nbsp}} V only PICs like the 18FJ, 24H, and 33F series use a special signature to enter programming mode and V<sub>pp</sub> is a digital signal that is either at ground or Vdd. There is no one V<sub>pp</sub> voltage that is within the valid V<sub>pp</sub> range of all PICs. In fact, the minimum required V<sub>pp</sub> level for some PICs can damage other PICs.
* ''' V<sub>dd</sub> ''' - This is the positive power input to the PIC. Some programmers require this to be provided by the circuit (circuit must be at least partially powered up), some programmers expect to drive this line themselves and require the circuit to be off, while others can be configured either way (like the Microchip ICD2). The Embed Inc programmers expect to drive the V<sub>dd</sub> line themselves and require the target circuit to be off during programming.
* ''' V<sub>ss</sub> ''' - Negative power input to the PIC and the zero volts reference for the remaining signals. Voltages of the other signals are implicitly with respect to V<sub>ss</sub>.