DS51795A Datasheet, PDF (72/98 Pages) Microchip Technology – PICkit™ 3 Programmer/Debugger

PICkit™ 3 User’s Guide
Additionally, MCLR is also used as either a high voltage programming signal or as an
attention indicator to the device.
In order to have trouble free in-circuit debugging, careful planning must be done by the
designer to avoid any problems during the application development or production
phase of the product.
RECOMMENDED CONFIGURATION
The signals PGC and PGD are active bidirectional signals driven by the PICkit 3 and
target emulation device. If these signals can be kept free from any other passive circuits
or active logic in the application, it will ensure trouble free debugging and programming
sessions. Also, cable length and/or type may be negligible with this configuration.
Additionally, the MCLR signal is used by PICkit 3 to provide the voltage used for pro-
gramming some devices or to signal attention. In instances where the application has
a large capacitor, it will cause the signal rise and fall time to degrade. This will hinder
the ability of PICkit 3 and the device to communicate effectively. It is recommended to
keep the signal pulled up to VDD with a 10K resistor, and to utilize the power-on timer
features of the device to ensure a proper power-up sequence.
ALTERNATE CONFIGURATION
In some cases, especially with low pin count devices, the pins must be utilized by the
application.
If this is the case, as a minimum, a resistive isolation is required between the device
and the application active node. This will ensure that both the application circuit and
PICkit 3 are able to drive the PGC or PGD node to ground and to the proper VDD levels.
Figure B-1 depicts this configuration.
FIGURE B-1:
TYPICAL ICSP™ APPLICATION CIRCUIT
The resistive isolation value will differ depending on the application and how it is being
used. Values ranging from 1K to 10K are suggested. In any case, ensure the levels on
PGD and PGC can be driven to their appropriate logic voltage levels.
COMMUNICATION CHANNEL
Some devices have the flexibility to use one of several communication channels or pins
for programming and debugging. These channels are generally referred to in data
sheets as PGCx/PGDx, where x is channel number identifier. These channels are often
multiplexed with some peripherals (I²C™, SPI, A/D). If your application uses those
DS51795A-page 68
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