ICD-U40 and similar

Guest · Posted: Sun Jun 04, 2006 7:19 am

Hi,

I'm trying to program a POC running at 3.3v using ICSP. My current programmer has ICSP, but says that it does not support LVP. However, I think what I am doing is not LVP, simply HVP at a low voltage (having grounded the LVP pin)

Can anyone clear up this confusing distinction between LVP, HVP, and HVP at a low voltage?

Also, what programmers do people recommennd. The ICD2 is very expensive - the CC ICD-U40 much cheaper, and there are countless others...

Cheers,

Ben

Ttelmah · Guest

It'd help if you said 'what PIC'. However you cannot 'ground the LVP pin' to change modes. A chip can _always_ be programmed using HVP, but will only accept LVP commands, if this is enabled in the configuration word. When HVP is used, the state of the LVP pin does not matter. The need to ground this pin, is if the chip is set to use LVP, and the pin is allowed to rise, it can accidentally go into program mode, hence it must be pulled down, for the chip to run. Now there is no such thing as 'low voltage HVP', on any PIC that I can think of. HVP, requires that an external source supplies the Vpp voltage, and this is normally a minimum of Vdd+3.5v. The normal reason for ICSP to fail, is if something is preventing the rails being held to their correct voltages. The MCLR line (this is normally the Vpp input), _must be able to rise above the Vdd voltage, and because the current available from most programmers is low, only a large resistor, may be used as a pull-up on this line. The resistor value recommended in the MicroChip notes, will not work with some programmers, that cannot deliver as much current as others. Typically something around 47K, is reliable with all programmers. Remebmer also that Vdd needs to be present on the chip toprogram it, and this needs to feed back out to the ICSP Vdd pin. Some progammers use this voltage to drive the buffers feeding the signals to the chip.

Best Wiishes

Guest · Posted: Sun Jun 04, 2006 5:16 pm

By Low Voltage HVP I meant that the programmer still provides a high voltage to the MCLR pin, but the PIC is powered from its own supply at <5V. This seems to limit the commands that can be issued (such as code protection fuses), but otherwise everything works as normal. However, some programmers don't seem to support programming at under 5v...