User manual

Theory of Operation

2.5.5 Circuits That Will Prevent the Debugger From Functioning

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

MPLAB ICD 3 in-circuit 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 kΩ 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.

2.6 DEBUGGING WITH THE DEBUGGER

There are two steps to using the MPLAB ICD 3 in-circuit debugger system as a

debugger. The first requires that an application be programmed into the target device.

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. Programming the code into the target and activating special debug functions

(see the next section for details).

2. Using the debugger to set breakpoints and run.

If the target device cannot be programmed correctly, the MPLAB ICD 3 in-circuit

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 V

DD and VSS lines from the

debugger are not shown.

No!

VPP/MCLR

PGC

PGD

Interface

Connector