matrixofdynamism
Advanced Member level 2
The document DS31028A page28-4 Figure 28-1 contains a diagram for connections of a "typical ICSP application circuit". It shows how ICSP is to be connected to a PIC. It shows connections for MCLRn/Vpp, VDD, VSS, RB6 and RB7. I have the following questions:
(1) How are resistor values determined. I have some schematic saying "atleast 10kohm".
(2) Are these resistors creating a barried between VDD and the signal applied by ICSP? I think this is so.
(3) The capacitor is used to "isolate vpp votlage from the rest of the circuit". How does this capacitor tied to ground achieve that?
(4) The diode is used to prevent flow of current towards VDD when VPP of 13V is applied during programming. Is that so? Why does this have to be a schottkey diode after all it is reverse biased during programming?
The document states "do not use RB6 and RB7" to simplify this interface. However, it talks of "isolation circuits" and buffers if they RB6 and RB7 are being used in application circuit.
(5) What does isolation circuit mean, is it merely a jumper?
(6) Since RB6 and RB7 are clock and data and only go upto 5V, what is danger of using them in application circuit? I assume that the problem is that using them will create capacative loading that shall limit the rise and fall times and cause programming to fail. And that is when we need a "buffer" to provide stronger drive to them. Is this correct?
As you can see, I have read the document and am only asking for clarification.
(1) How are resistor values determined. I have some schematic saying "atleast 10kohm".
(2) Are these resistors creating a barried between VDD and the signal applied by ICSP? I think this is so.
(3) The capacitor is used to "isolate vpp votlage from the rest of the circuit". How does this capacitor tied to ground achieve that?
(4) The diode is used to prevent flow of current towards VDD when VPP of 13V is applied during programming. Is that so? Why does this have to be a schottkey diode after all it is reverse biased during programming?
The document states "do not use RB6 and RB7" to simplify this interface. However, it talks of "isolation circuits" and buffers if they RB6 and RB7 are being used in application circuit.
(5) What does isolation circuit mean, is it merely a jumper?
(6) Since RB6 and RB7 are clock and data and only go upto 5V, what is danger of using them in application circuit? I assume that the problem is that using them will create capacative loading that shall limit the rise and fall times and cause programming to fail. And that is when we need a "buffer" to provide stronger drive to them. Is this correct?
As you can see, I have read the document and am only asking for clarification.
