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DEMYSTIFYING IN-CIRCUIT SERIAL PROGRAMMING

by Phil Anderson

Start ı Humble Beginnings ı Application Circuit Example ı The End Result ı Sources and PDF

HUMBLE BEGINNINGS

As I mentioned, when I first read all of the selected datasheets and application notes on ICP, it seemed confusing, so I took it step by step.

The notes say I have a choice: use high or low voltage programming, depending on the state of the LVE configuration bit. Whatıs that about? If I use low voltage (i.e., 5 V) then I wonıt need to provide a high voltage. However, I see that if I use a low voltage for programming I must dedicate an I/O line to control that. In most cases, I donıt wish to do that.

Now, it started to make sense. If I use a high voltage on pin 1, Iıll have to isolate the application circuit from that pin to prevent damage. Also, I guess I need to keep the application circuit from loading V_DD supplied by the chip programmer, because the programmer doesnıt supply much current. And, I have to make sure the clock and data pins donıt have too much capacitance on them, otherwise theyıll slow down the programming pulses.

In addition, one application note included an ICP programming interface. I wondered, at first, if this was a requirement for ICP. After some study, I saw that it depends.

If your circuit cannot be isolated from the chip to be programmed, then a special programming interface is indeed required. Rise times for the clock and data lines must be preserved. However, if the application circuit can be isolated easily, then a chip programmer does just fine.

So, where did that leave me? Letıs cut through all the red tape and application notes. Letıs demystify ICP. First, note that chip programming and ICP are essentially "the same thing. Here are their similarities.

With care, you can use your chip programmer for ICP. For example, if you're working with a ı16F873, you can use your PICSTART PLUS programmer and MPLAB. In addition, the data format is the same. The file format for chip programming and ICP is the same. It always was the same. ICP issues simply deal with circuit loading of the programmer interface. Your chip programmer was not designed to drive application circuits.

Also, your programmer supplies the same signals called for in an ICP programmer. The microcontroller chip demands the same signals for programming, regardless of whether it is in or out of a circuit during programming. Lastly, if the chip soldered in the circuit can be electronically isolated and cabled to your programmer, you can program it in-circuit. This fact says it all. If the chip is isolated and the cabling is kept short, the assembly is the same as if the chip was originally placed in the programmer. Itıs the same thing. Oh! The datasheet didnıt say that?

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