In PIC12C5XX programming guide I found a requirement:

1.1 Hardware Requirements

The PIC12C5XX requires two programmable power supplies, one for V_DD (2.0V to 6.5V recommended) and one for V_PP (12V to 14V). Both supplies should have a minimum resolution of 0.25V.

What does it mean?

I found an article on power supply resolution versus accuracy, and it boils down to:

Our power supplies use Digital to Analog Converters (DACs) to take the user inputted settings and convert them to analog signals that set a programming voltage that will interact with the control loop of the power supply to set the output. The resolution supplemental characteristic represents one single count of the DAC.

Which means it applies to power supplies where the user sets the voltage; minimum step by which the voltage can be changed. Now in the guide we have a pretty loose requirements for preset voltages, no requirement for them to be changeable by the user. I really don't see any application of supply resolution as explained by the article. The basic requirements look like if I apply 5V and 13V with accuracy +-1V I should be set. So what does the resolution mean in this context?

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    \$\begingroup\$ The two excerpts have nothing to do with each other. The PIC requirements are just poorly stated. In fact you do not need programmable supply. And resolution means nothing without accuracy. \$\endgroup\$ – venny Aug 23 '14 at 11:59
  • \$\begingroup\$ @venny resolution can be useful without \$\endgroup\$ – Chris Stratton Aug 23 '14 at 15:42

A programmable supply is required to make a production programmer for these PICs, because production verification must be done at both minimum and maximum Vdd for the part.

There are requirements for both accuracy and resolution of the programming, however the document does not actually specify what the tolerances are, just that it must be verified 'at' the minimum and maximum voltages, which is clearly an impossible condition to meet.

It's left up to the implementor whether it's better to fudge the maximum and potentially compromise the programming verification or vice versa (or just aim for the nominal and let the the chips fall where they may, so to speak).

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The PIC programming guide really SHOULD have used a different word there: "tolerance". They're just pointing out that the supply voltage shall be within 0.25V of nominal.

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  • \$\begingroup\$ I don't agree. The tolerance appears to be explicit, e.g. "12V to 14V". Also there is no 'nominal' value to apply the 0.25V to. What is the 0.25V being applied to, 12V and 14V? That isn't possible simultaneously. I think venny is correct; it is "poorly stated". \$\endgroup\$ – gbulmer Aug 23 '14 at 16:33

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