51795B datasheet(21/100 Pages) MICROCHIP

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Theory of Operation

 2010 Microchip Technology Inc.

DS51795B-page 21

2.4.5

Circuits That Will Prevent the Debugger From Functioning

Figure 2-5 shows the active debugger lines with some components that will prevent the

PICkit 3 debugger system from functioning.

FIGURE 2-5:

IMPROPER CIRCUIT COMPONENTS

Specifically, these guidelines must be followed:

• Do not use pull-ups on PGC/PGD – they will disrupt the voltage levels, since

these lines have 4.7 k

 pull-down resistors in the debugger.

• Do not use capacitors on PGC/PGD – they will prevent fast transitions on data

and clock lines during programming and debug communications.

• Do not use capacitors on MCLR – they will prevent fast transitions of VPP. A

simple pull-up resistor is generally sufficient.

• Do not use diodes on PGC/PGD – they will prevent bidirectional communication

between the debugger and the target device.

2.5

DEBUGGING

There are two steps to using the PICkit 3 programmer/debugger system as a debugger.

The first requires that an application be programmed into the target device (usually with

the PICkit 3 itself). The second uses the internal in-circuit debug hardware of the target

Flash device to run and test the application program. These two steps are directly

related to the MPLAB IDE operations:

1. Program the code into the target and activate special debug functions (see the

next section for details).

2. Use the debugger to set breakpoints and run.

If the target device cannot be programmed correctly, the PICkit 3

programmer/debugger will not be able to debug.

Figure 2-6 shows the basic interconnections required for programming. Note that this

is the same as Figure 2-4, but for the sake of clarity, the VDD and VSS lines from the

debugger are not shown.

No!

VPP/MCLR

PGC

PGD

Interface

Connector

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