3.4.2.1 Disabling J-Link-OB (ATSAM3U4C)

Jumper J7 disables the J-Link-OB-ATSAM3U4C JTAG functionality. When the jumper is installed, it grounds pin 25 (PA26) of the ATSAM3U4C that is normally pulled high.

  • Jumper J7 not installed: J-Link-OB-ATSAM3U4C is enabled and fully functional.
  • Jumper J7 installed: J-Link-OB-ATSAM3U4C is disabled and an external JTAG controller can be used through the 10-pin JTAG port J11.

Jumper JP9 disables only the J-Link functionality. The debug serial com port that is emulated through a Communication Device class (CDC) of the same USB connector remains operational (if J9 is open).

Figure 3-37. Enabling/Disabling J-Link-OB and J-Link-CDC

Jumper J7 disables the JTAG functionality only. The debug serial com port that is emulated through a CDC of the same USB connector remains operational.

When J7 is on and the J-Link-OB-ATSAM3U4C JTAG disabled, the JTAG function is available through connector J11. A quad analog switch (NLAS3899B) is used to select and isolate the JTAG interface.

Table 3-19. J-Link-OB and J-Link-CDC Jumper J7 Settings
Jumper J7 J-Link-OB JTAG MPU
Open Active Inactive
Closed Inactive Active
Table 3-20. J-Link-OB and J-Link-CDC Jumper J9 Settings
Jumper J9 J-Link-CDC
Open Active
Closed Inactive
Figure 3-38. JTAG Switch