Atmel AVR042, Примечание к применению

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AVR Hardware Design Considerations [APPLICATION NOTE]
Atmel-2521M-AVR-Hardware-Design-Considerations_ApplicationNote_092014
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Figure 3-5. Filters on JTAG Pins – Correct and Incorrect Ways to Connect
3.3 PDI Interface
The Program and Debug Interface (PDI) is an Atmel proprietary two-line interface that was introduced with the
Atmel AVR XMEGA
®
microcontroller family. As the name implies, this interface can be used for both In-System
Programming and on-chip debugging of devices.
Figure 3-6 shows the standard PDI connector supplied with Atmel programmers. Only two pins on the device are
needed for use of this interface: RESET, also called PDI_CLK, and the dedicated PDI_DATA pin. The target’s
voltage supply is made available to allow for powering of the device or ensuring correct signal levels during
programming.
Figure 3-6. Standard PDI Connector Used on e.g. Atmel STK600 and AVR JTAGICE mkll
3.3.1 External Reset Circuitry
Since the RESET line is used for clocking the PDI, it is important to bypass or avoid any circuitry that can distort
the clock signal during programming or debugging, such as capacitors and external reset sources. During normal
operation the RESET pin has an internal filter to prevent unintentional resets, e.g. caused by short spikes on the